WO2019068960A1

WO2019068960A1 - Method of modifying feather raw material

Info

Publication number: WO2019068960A1
Application number: PCT/FI2018/050708
Authority: WO
Inventors: Anne Kallioinen; Jouko Savolainen
Original assignee: Hkscan Oyj; Uniq Bioresearch Oy
Priority date: 2017-10-02
Filing date: 2018-10-02
Publication date: 2019-04-11
Also published as: FI127941B; FI20175869A1

Abstract

The present invention is directed to a method of modifying feather raw material comprising the steps of: (a) treating feather raw material in a first aqueous solution containing sulphite ions, wherein the treatment is carried out at pH 6 –8, reaching temperature of about 90 degrees Celsius, the treatment lasting at least 30minutes; (b) separating the sulfonated feather material obtained from step (a);(c) treating the sulfonated feather material in a second aqueous solution, wherein the treatment is carried out at pH 1.5 –3.0 and at temperature of 10 –30 degrees Celsius, the treatment lasting at least 5 minutes;and (d) adjusting the pH of the second aqueous solution or the feather material obtained from the second aqueous solution to at least pH4.5 –5.5.The produced protein-rich modified feather product is suitable as an additive for use, e.g., infood industry, animal feeds and cosmetics.

Description

Method of modifying feather raw material

FIELD OF THE INVENTION

The present invention relates to the fields of meat industry and the production of protein- containing ingredients. Particularly, the present invention is directed to the use of feathers, a byproduct of chicken meat production, for producing a protein-rich additive suitable for animal feeds, food industry, cosmetics products, packaging materials and also for coating or building materials such as cement and paints.

BACKGROUND OF THE INVENTION

Feathers contain keratin protein as a main component. Keratin is rich in disulfide bonds (i.e. disulfide bridges) that stabilize the structure and make it durable and rather difficult to digest and degrade. Keratin is also known to be highly insoluble in water. Only part of keratin can be enzymatically hydrolyzed by conventional proteases and it is also the reason why it is digested by animals rather poorly. Methods to increase digestibility and hydrolysis of keratin have thus been developed including chemical treatments as well as enzymatic treatments (see Pedersen et al., 2012; Staron et al., 2014; and Khosa and Ullah, 2013).

In EP 1731528, a mixture of water and keratin is hydrolyzed by alkali at 80-120 °C for 1 to 16 hours and then neutralized to obtain a solubilized keratin. EP 2832236 describes a process, where keratinous material is hydrolyzed at elevated temperatures at pressures from about 2 bar to about 10 bar. The resulting hydrolyzed keratinous material is dried at temperatures below 90 °C to maintain the pepsin digestibility above 85%. In US

2012/0219667, a method producing soluble keratinous protein by treating keratin in oxidizing solution in low pH and heat is described. The oxidizing solution can be e.g.

performic acid, peracetic acid or peroxide. The oxidizing step is followed by raising the pH to the pK_a of the proteins or to the point proteins are present in the salt form. The resulting protein solution can be used as nutritional supplement.

Further, EP 0499260 discloses sulphite treatments of feather material at 60-100°C and pH 6-9 for 10 minutes to 4 hours. The treated sulfonated feather mass was subsequently hydrolyzed by proteolytic enzymes into keratin hydrolysate and then concentrated. Ash content of the dry matter as high as 8.5% was reported. A use of the keratin hydrolysate as animal feed was suggested. In WO 0301 1894, a process consisting of oxidative

sulphitolysis as a first stage and extraction by controlled washing by water as a second stage is described. The resulting keratin derivatives are high molecular weight soluble proteins that can be used in biopolymer applications. US 2015/0152153 discloses a combined treatment by a reducing agent and a proteolytic enzyme, where the treatment with the reducing agent can be after, during or prior to the protease treatment. The hydrolyzed keratin produced by the method was suggested for use in animal feed.

Large quantities of feather are produced by poultry industry as a side stream. Usually, feathers are used in animal feed after high temperature treatments when the digestibility might be higher but part of amino acids are degraded decreasing the feed value. It is protein rich material that has a high potential commercial value and therefore cost efficient technologies suitable for industrial production that increase the digestibility in relatively mild temperature conditions and without harming amino acid composition are needed. One problem with the treatments with chemicals is often the resulting high salt concentrations that are not acceptable in food or feed products, and require excessive and often rather expensive downstream processing such as ultrafiltration to remove salts. The present invention is thus directed to the production of a feather-based ingredient with high protein content and low salt concentration. SUMMARY OF THE INVENTION

The aim of the present invention is to modify durable and rigid feather keratin by improved reductive sulphitolysis reaction and pH adjustment steps to increase hydrolysability of feather keratin and in this way produce a protein-rich multipurpose additive.

The present invention is directed to a method of modifying feather raw material comprising the steps of:

(a) treating feather raw material in a first aqueous solution containing sulphite ions, wherein the treatment is carried out at pH 6 - 8, reaching temperature of about 90 °C, the treatment lasting at least 30 minutes;

(b) separating the sulfonated feather material obtained from step (a); (c) treating the sulfonated feather material in a second aqueous solution, wherein the treatment is carried out at pH 1.5 - 3.0 and at temperature of 10 - 30 °C, the treatment lasting at least 5 minutes; and

(d) adjusting the pH of the second aqueous solution or the feather material obtained from the second aqueous solution to at least pH 4.5 - 5.5. Another aim of the present invention is to provide a protein-rich modified feather product produced by the method as described above.

Another aim of the present invention is to provide a nutritional additive for animal feeds produced by the method as described above and also an animal feed comprising said nutritional additive.

Another aim of the present invention is to provide a protein-rich nutritional supplement for food industry produced by the method as described above and a food-product comprising said supplement.

Further aims of the present invention are the provision of a cosmetic ingredient, component for making improved packaging materials, or an additive for coating or building materials comprising the modified feather material manufactured by the method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Examples of process steps for feather modification.

Figure 2. (A) Untreated feather material and (B) modified dried feathers. Treatment was carried out as defined in the Experimental Section below in Lodige reactor at 90 °C, pH 7 for 40 min with sodium metabisulphite 0.225 g / g dry matter.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, significant increase in enzymatic hydrolysability of feather material can be obtained by the feather modification treatments disclosed herein compared to untreated feather and also to previous modification methods of the prior art. The protein content of the final modified feather powder product can be as high as 97% while ash content is only 0.4% of dry matter (w/w). The final product thus showed efficient washing of salts. Total bacteria content was below 40 CFU/g of dry matter and thus microbiological quality was good. In addition, free SH-groups of the final product are found to be

antioxidative and thus have other health promoting effects.

Accordingly, the present invention provides a method of modifying feather raw material comprising the steps of:

(a) treating feather raw material in a first aqueous solution containing sulphite ions (to perform a sulfito lysis), wherein the treatment is carried out at pH 6 - 8, reaching temperature of about 90 °C, the treatment lasting at least 30 minutes;

(d) adjusting the pH of the second aqueous solution or the feather material obtained from the second aqueous solution to at least pH 4.5 - 5.5.

In the first step of the modification, i.e. step (a), the feather raw material is subjected to sulfito lysis. In this step, cleavage of disulfide bonds in feather keratin structures and modification of conformation are accomplished by sulfito lysis where a sulphite ion reacts specifically with one sulfur in the disulfide bond forming an S-sulfonate derivative. The other sulfur is reduced to a sulfhydryl group. The reagent that forms sulfite ions, preferably a sulphite salt, can be, e.g., soluble and food-grade sodium sulphite Na₂S03, sodium hydrogensulphite NaHSC"3 or sodium metabisulphite Na₂S₂0₅. The dry matter content of the feather raw material in the solution is preferably in the range of 5 to 15% (w/w). In an embodiment, the feather raw material is chopped or grinded to a smaller particle size before the treatment. The first aqueous solution is preferably water and the feather raw material, e.g. chicken or turkey feathers, is mixed to the solution in a reaction vessel. Said feather raw material can be initially chopped or ground to smaller particle size. In a preferred

embodiment, the sulphite salt is added to the mixture so that the sulphite content corresponds to the amount of sulphite provided by 0.15 - 0.25 g metabisulphite / g of feather raw material (dry matter). In a preferred embodiment, the sulphite content varies from 5 to 25% (w/w) dry matter in relation to the amount of feather raw material present in the first modification step, e.g. a preferred concentration of sulphite in the mixture, i.e. the first aqueous solution, is at least 0.1 M, more preferably between 0.1 - 0.2 M. If required, pH is adjusted to the range of pH 6 - 8, preferably pH 6.5 - 7.5 or more preferably to about pH 7, for instance by using NaOH solution. After pH adjustment, the treatment is started by heating the reactor. Treatment time is at least 30 min, preferably at least 35 or at least 40 min, more preferably 30-60 min. During the treatment, temperature is raised to about 90°C and then preferably controlled at 87-90°C, e.g. by using steam. The suspension in the reactor is preferably continuously mixed during the treatment. In the first separation step, i.e. step (b), advantageously performed by filtration and preferably comprising a further washing step or washing steps, the sulfonated feather material is separated from the reaction solution to remove unreacted sulphite ions.

Preferably, the removed sulphite in the form of sulphite rich washing water is recycled and used again in the first step of the present method. The separation/washing step also increases the process safety as during the following step the pH is adjusted to pH 1.5 - 3.0, preferably to pH 2.0-3.0, and toxic gas, sulphur dioxide is formed. In a preferred embodiment, several batches of feather are collected in step (b) and treated subsequently in step (c).

In the second treatment step, i.e. step (c), the sulfonated feather material is mixed with a second aqueous solution, preferably water, wherein the pH is adjusted to the range of pH 1.5 - 3.0, e.g. by adding hydrochloric acid. The treatment lasts at least 5 minutes, preferably 5- 10, 5-15 or 5-20 minutes and is performed so that the suspension's temperature is in the range of 10 - 30 °C, preferably 15 - 30 °C. At acidic conditions, sulphur dioxide is released from the sulphonated feather material as well as from the remaining unreacted sulphite reagent. The second treatment step thus results feather material with free sulfhydryl groups. Reactor suspension is also preferably continuously mixed during the second treatment.

In the following step, i.e. step (d), the pH is adjusted, preferably by using NaOH solution, to at least pH 4.5 - 5.5, preferably to pH >5, more preferably about pH 5. While increasing the pH, the remaining sulphur dioxide in the feather material is dissolved as sodium sulphite in the second aqueous solution.

For efficient washing of salts from the treated feathers, the material is preferably separated or filtrated from the second aqueous solution after the pH adjustment and subsequently mixed or immersed with water for washing the salts. In a preferred embodiment, the separation and washing steps are repeated at least once. To obtain a powdered final product, milling of the feather material obtained from the previous steps can be carried out either by wet or dry milling, e.g. by a conical mill. Wet milling requires that modified feather can be pumped from the reaction vessel. Drying of the feather material thus obtained can be performed by the methods well-known in the art, such as vacuum drying, jet drying or freeze drying. Milling as dry is also possible in a process scale.

The present method may also comprise a further step of enzymatic hydrolysis. This stage is preferably performed after the milling step. For the hydrolysis reaction in an aqueous solution or buffer, the pH is controlled to be in the range of 6 to 10. The temperature is set from 30 to 80 °C, being dependent on the enzyme used. Appropriate enzymes are the neutral and alkaline proteases, preferably mixes of proteases, from different manufacturers, such as Alcalase 2.4L FG (Novozymes, Denmark). The amount of the enzyme is dispensed mainly by the amount of activity required. The amount of activity is determined mainly according to manufacturer's instructions and the amount of substrate and the desired hydrolysis time. In a preferred setting, the step of enzymatic hydrolysis is performed in consecutive reactors each reactor comprising a separate protease or a separate mix of proteases to perform a step-by- step hydrolysis.

The present invention is also directed to a protein-rich modified feather product produced by the method as defined above and to an animal feed comprising said product. Preferably, said product comprises powdered feather material having protein content more than 90% and ash content less than 1.5% (w/w), preferably less than 1.0% (w/w). In another preferred embodiment, said product is not enzymically treated, more preferably not protease-treated, in order to produce an undigested high-molecular- weight protein fraction which is essentially insoluble to water. Further, in other preferred embodiments, the product prepared with the method of present invention can be distinguished from other powdered feather materials based on the amount of free carbon-bonded sulfhydryl (R-SH) groups present in the modified feather product. For example, when comparing the average amount of SH groups present in the modified product and in powdered raw feather material, the amount is significantly higher in the modified product (see the Experimental Section below). A preferred molar concentration range for free SH groups in the modified product is more than 55, 56, 57, 58, 59 or 60 μιηοΐ/g. Other preferred ranges for free SH groups in the modified product are selected from the group consisting of 59-61, 58-62, 57-63, 56-64, and 55-65 μιηοΐ/g. More preferably, said product comprises modified feathers as the only protein source. As shown below in the Experimental Section, said powdered feather material also has higher enzymatic hydro lysability compared to untreated feather material.

The present invention is further directed to a nutritional additive comprising said protein-rich modified feather product. Said nutritional additive can be used as a supplement or ingredient of an animal feed suitable for improving animal health. The feed for poultry or pigs, for instance, may include wheat, corn or soybean and the feed for a ruminant is typically hay or live grass. In order to increase the protein-content of the feed, the nutritional additive of the present invention is added to the feed in granular, powdered, pellet, tablet, or other form, preferably as powder. In a preferred embodiment, the nutritional additive of the present invention is used as an ingredient of a ready-made animal feed product or feed additive product.

In principle, the resulting dried and milled protein-rich modified feather product is also suitable as food supplement for dissolving into liquid such as juice, milk, beverage or a nutritional drink, for sprinkling on food or mixing with other food ingredients. The disclosed protein-rich modified feather product is suitable for protein supplementation for any purpose including, but not limited to, dietary supplements. The protein-rich modified feather product can also be provided as tablets, powders or incorporated into bars. The present invention is thus also directed to food products comprising the nutritional additive as defined above.

Further, the invention relates to a cosmetic additive comprising the protein-rich modified feather product manufactured by the above-described method. The protein-rich modified feather product is expected to be blended in cosmetic products, such as hair cosmetics (for example, shampoos and hair conditioners), and skin-care products such as creams, lotions and ointments.

The cosmetic additive of the invention consisting of the protein-rich modified feather product can be blended together with various cosmetic ingredients, including various surface active agents such as anionic/cationic/nonionic surface active agents, synthetic polymers such as polyethylene glycol and propylene glycol, humidity retaining agents such as glycerin and butylene glycol, oil solutions such as animal and vegetable oil, ester oil, higher alcohols and lower alcohols, silicone oil, animal and vegetable originated protein such as collagen, as well as preservatives and perfumes.

Feather-based ingredient can be incorporated in environmentally friendly packaging materials for improving their physicochemical properties. These include for example improved mechanical and barrier properties, water resistance, and biodegradability (see Gomez-Estaca et al, 2016). In another embodiment, the protein-rich modified feather product obtained by the present method is an additive for coating or building materials such as cement or paint. The modified feather product may provide increased density, viscosity, shortened drying time for cement and reduced volatile organic (VOC) content, better film- forming properties, better water resistance, and low toxicity for paints. The publications and other materials used herein to illuminate the background of the invention, and in particular, to provide additional details with respect to its practice, are incorporated herein by reference. The present invention is further described in the following Experimental Section, which is not intended to limit the scope of the invention.

EXPERIMENTAL SECTION

Materials and methods

Raw materials Feather raw material was obtained from poultry production plant. The dry matter content of feather was about 50%. Two batches of raw material were obtained from HKScan. As a sulphite reagent, sodium metabisulphite was used.

Laboratory scale treatments of feathers

Laboratory scale experiments were carried out in a 10 1 steel vessel equipped with a mixer. 500 g of feathers (250 g DM) were suspended totally in 5 1 of water and heated to reaction temperature. Three different temperatures, 70°C, 80 °C and 90°C, were tested as well as two different pHs, pH 6.5 and pH 7.0. Sodium metabisulphite dosages of 0.14-0.2 g/g dry matter (DM) were applied.

Reaction time was 40 min. After reaction, pH was decreased to pH 2.0 and then pH was raised to pH 5.0. After pH adjustments, feather was washed. Feather was separated from the suspension by filtering through a sieve. A clear but yellowish filtrate was obtained. Sample of the filtrate was taken to analyse DM and ash contents. Feathers were washed, filtrated again and dried in a heating chamber for overnight.

Small pilot scale treatments of feathers

Small pilot scale experiments were carried out in a 40 1 steel tank. 4 kg of feathers (2 kg DM) was added to 38 1 of water and was heated to 90 °C. Sodium metabisulphite (0.225- 0.250 g/g DM) was dissolved in of water and added to feather suspension and pH was adjusted to pH 7.0. Reaction time was 40 min. After reaction time, feather slurry was cooled and then filtrated through a sieve to separate feather from filtrate. Feathers were re- suspended in water and pH was adjusted to pH 2.0. Sulphur dioxide was released in this reaction. Feathers were filtrated again, re-suspended in water, mixed thoroughly, filtrated again and then dried. A sample of the last filtrate was taken for DM and ash content assays. Large pilot scale production of activated feathers

In the large pilot scale treatment of activated feathers, a 600 1 Lodige vertical reactor was used. Reactor was loaded with 55.2 kg feather (dry matter content 46.5%) and 480 1 water. 5.67 kg of sodium metabisulphite was dissolved in 20 liters of water and added to reactor. pH was adjusted to pH 7 by 50%> NaOH solution. After pH adjustment, reactor was heated to 90 °C. During reaction, temperature was controlled at 87-90°C. Mixing was 85 rpm. In addition, two homogenizers were mixing at 1500 rpm. After 40 min reaction time, cooling was started by circulating cold water in the reactor jacket. The activated feather suspension was drained on a fibre cloth in an IBC container. The filtrate was removed and feather was collected into plastic bags. A sample of the filtrate was taken. 300 1 of water and the filtrated feather were added back into the reactor. The pH of the feather suspension was adjusted to pH 2 by 33% HC1. After 5 min mixing time, pH was adjusted to pH 5 by adding 50% NaOH. After that, feather suspension was drained on a fibre cloth and washed with water. After removal of filtrate, feather was washed with water and drained again on fibre cloth. The feather was left overnight at 16-17 °C on fibre cloth to remove water from it.

Feather was dried by vacuum evaporation in Lodige reactor. Product temperature varied between 21 °C and 27 °C, and the pressure was 24-36 mbar. Samples were taken to follow drying. Total drying time was 5.5 hours. The material was collected into plastic bags. After drying, feather was ground by a conical sieve mill.

Analysis methods

Before analyses, dried feather sample was cut by a kitchen chipper having a rotating knife to homogenize the sample. Enzymatic hydro lysability of keratin protein was analysed by hydro lysing modified feather by a commercial proteolytic enzyme mixture Alcalase 2.4L FG (Novozymes, Denmark) at 1% dry matter (DM) content. 2.5 g of feather sample was dissolved in 247.5 ml of 0.05 M sodium phosphate buffer pH 7.5. 50 μΐ of Alcalase was added to start the reaction. Reaction was carried out in Erlenmeyer flasks at 55 °C. Flasks were shaken at 170 rpm for mixing during reaction. Samples were taken during hydrolysis to follow the reaction. Reaction was stopped by adding 1 M HC1 to drop pH below pH 4.0. After 4 h hydrolysis, the remaining solid material was filtered through Whatman 40 filter paper, filter cake dried and weighted, and the degree of solubilisation was calculated. In addition, for 25 μΐ of hydrolysis sample, 2 ml of OP A (o-phtalaldehyde) reagent was added, mixture vortexed and after 2 min incubation in room temperature, the formed absorbance was detected spectrophotometrically by using 340 nm wavelength. The free a-amino-groups in hydro lysed protein react with OPA reagent and form ultraviolet colour and the intensity of the colour was measured. As a reference, untreated, water rinsed feather was hydrolysed and analysed. Analyses were carried out as duplicates. Nitrogen content in the feather samples was analysed by a Kjeltec analysator based on the Kjeldahl method. Protein content was calculated from the nitrogen content by multiplying by 6.38. Ash content was analysed by drying the sample at 102 °C for 16 h (Dry matter content) and then heated at 550 °C for 19-22 h.

Total bacteria content of treated feathers was analysed. Feather was mixed thoroughly for 30 min with saline solution and a diluted sample was cultivated on plate count agar plates for 2- 3 days at 30 °C. The formed colonies were calculated and result presented as colony forming units (CFU).

An assay for free SH group content of treated feather compared to untreated but intensively ground and milled powdered feather material was conducted with Ellman's reagent as described by Chan and Wasserman, 1993. Ellman's reagent, 5,5'-dithiobis (2-nitrobenzoic acid) reacts specifically with carbon-bonded sulfhydryl (R-SH) groups present in the assayed material.

Results and discussion

General remarks from feather treatments

The aim of the feather treatments was to modify durable and rigid feather keratin by reductive sulphitolysis reaction. Feather was treated with sodium metabisulphite in water solution at 70-90 °C, pH 6.5-7.0 for 40 min. 5% DM content was selected for the experiments to get proper mixing for rather viscous feather suspension throughout the reaction.

In all experiments, already 10 min after the beginning of reaction, the feather suspension started to change and was more freely flowing. The appearance of feather material also changed during treatments. Feather mass absorbed quite much water and the dry matter content after washing (and pressing by scoop) was quite low, approximately 17-19%.

Enzymatic hydrolysability

To determine the effect of sulphitolysis treatments on the digestibility of feather, enzymatic hydrolysability of feather was analysed. The test system consisted of treatment of feather with Alcalase commercial protease for 4 hours. The hydrolysability and hydrolysis result was analysed by two different methods: by hydrolysis residue filtration and by a

spectrophotometric method.

Spectrophotometric method was based on the reaction of free amino groups with OPA reagent and the reaction product could be detected by spectrophotometric measurement using 340 nm wavelength. Absorbance measurements showed that the increasing temperature in feather treatment increased the formation of free amino-groups and thus hydrolysis of keratin. In addition, increase in sulphite dosage (from 0.14 up to 0.225g/g DM) also showed some increase in hydrolability. Result showed that the highest tested sulphite dosage, 0.250 g/g, showed no further improvement in hydrolysability. Filtration method was applied to determine the amount of feather that could be dissolved by enzymatic treatment. Similarly to spectrophotometric analysis, filtration method showed that increasing temperature in feather modification increased dissolution of feather in enzymatic hydrolysis. The highest dissolution of feather material, 47%, was obtained with large pilot scale experiment at 90 °C. For the untreated feather, the dissolution in hydrolysis was typically 25-26%, but some variations in the dissolution of different feather batches were detected. Especially reference for the experiment at 70° C had 35% dissolution compared to other untreated samples. No significant differences were seen between the treatments at 90 °C with 0.225 and 250 g/g sulphite dosages. Based on the hydrolysis results, 90 °C, pH 7.0 and sulphite dosage of 0.225 g/g DM was selected for large pilot scale experiment. Protein, ash and bacteria contents

Protein content was analysed for modified feather after different treatments and for untreated feather. For untreated feather, protein content was analysed to be 93% of DM whereas for treated feather 92-95%. Thus only small changes in protein content were caused by feather modification treatments. Ash content, i.e. mineral content, was analysed from feather, filtrates and washing waters to assure that added sulphite reagent and other salts formed in pH adjustments are adequately removed by the washing procedure. In ash analysis, the modified feathers typically showed yellowish residue indicating that ashing was not fully complete although longer heating times were also tested. Thus, the presented ash content values for modified feathers might be higher than the true value. The ash content for untreated feather was 2.7% whereas for modified feathers 0.1-1.3%. Thus, results showed that untreated feather had higher ash content than all the modified feather samples. The first filtrates i.e. the sulphite solution separated from feathers after reaction, contained naturally increasing amounts of ash with increasing added sulphite. The last washing water for all experiments contained ash only 0- 0.1%). Thus the washing procedure carried out was adequate for removal of salts.

Sodium metabisulphite is an antimicrobial substance and is used as food preservative and therefore it was likely that the bacteria content of modified feather samples was low. Even though feather was treated and handled in a normal laboratory room, the analysed bacteria content was very low, below the detection limit 40 CFU/g of feather DM. The result indicates good microbiological quality.

Assay results for free SH group content Amount of free SH group content was analysed for modified feather and for untreated but intensively ground and milled powdered feather: molar concentration of SH groups (nmol/mg) Treated feather powder 61 ± 3

Finely ground raw feather 21 ± 4 The free SH group content of the treated feather powder was significantly higher compared to untreated finely ground raw feather material. Zhao et al., 2012, disclose that untreated feather contained only about 5 nmol of free SH groups per mg of the raw feather material but after subjecting the raw material to high density steam flash-explosion method, the level of about 25 nmol/mg was achieved. In view of Zhao et al., the effect of the present method is clear. Our result for the finely ground raw feather also implies that the amount of free SH groups may increase by intensive grinding and milling of the raw material.

Modification process

Based on the experiments, a process for feather treatments was developed (Figure 1).

Preferred process consists of sulphito lysis, pH adjustments, filtration and washing steps as well as milling and drying of feather material.

Sulphitolysis preferably includes the reaction of feather in 5 % DM content with sodium metabisulphite dosage of 0.225 g/g DM at 90 °C, pH 7 for 40 min. The first filtration (Figure 1) is carried out to remove the unreacted sulphite so that it can be recycled. In addition, the sulphite rich washing water could potentially be recycled and reused, and could replace partly the rather high initial sulphite dosage. REFERENCES

Cited patent document:

EP 1731528 EP 0499260

EP 2832236

US 20120219667

US 20150152153

WO 03011894 Cited scientific articles:

Chan, K-Y and Wasserman, BP., 1993. Direct Colometric Assay of Free Thiol Groups and Disulfide Bonds in Suspensions of Solubilized and Particulate Cereal Proteins. Cereal Chem. 70(l):22-26.

Gomez-Estaca, J., Gavara, R., Catala, R., Hernandez-Munoz, P., 2016. The Potential of Proteins for Producing Food Packaging Materials: A Review. Packag. Technol. Sci. 29, 203- 224

Khosa, M.A., Ullah, A., 2013. A sustainable role of keratin biopolymer in green chemistry: a review. J. Food Processing & Beverages 1 (1) 1-8.

Pedersen, M.B., Yu, S., Plumstead, P., Daalsgaard, S., 2012. Comparison of four feed proteases for improvement of nutritive value of poultry feather meal. J. Anim. Sci. 90, 350- 352.

Staron, P., Banach, M., Kowalski, Z., Staron, A., 2014. Hydrolysis of keratin materials derived from poultry industry. ECOpole'13 Conference, Jarnoltowek, 23-26.10.2013.

Proceedings of ECOpole 8 (2) 443-448. Zhao, E., Yang R., Zhang Y., Wu. L. (2012) Sustainable and practical utilization of feather keratin by an innovative physicochemical pretreatment: high density steam flash-explosion, Green Chem., 14, 3352-3360.

Claims

1. Method of modifying feather raw material comprising the steps of:

(b) separating the sulfonated feather material obtained from step (a); characterized in that the method comprises the further steps of:

(c) treating the sulfonated feather material in a second aqueous solution, wherein the treatment is carried out at pH 1.5 - 3.0 and at temperature of 10 - 30 °C, the treatment lasting at least 5 minutes; and

2. The method according to claim 1 further comprising the step of:

(e) separating the feather material obtained from step (d).

3. The method according to claim 2 further comprising the step of:

(f) wet milling the feather material obtained from step (e).

4. The method according to claim 3 further comprising the step of:

(g) drying the feather material obtained from step (f) to prepare modified feather powder.

5. The method according to claim 1 or 2, wherein the feather material obtained from step (e) is first dried and then milled as dry to prepare a powder. WO 2019/068960 ^λ=^> PCT/FI2018/050708

6. The method according to any of claims 1-5, wherein said feather raw material provided for step (a) is chopped or ground feathers, preferably chopped or ground chicken feathers.

7. The method according to any of claims 1-6, wherein the first aqueous solution contains an amount of sulphite corresponding to 0.15 - 0.25 g metabisulphite / g of feather raw material (dry matter).

8. The method according to any of claims 1-7, wherein in step (c) the second aqueous solution is water.

9. The method according to any of claims 1-8, wherein several batches of feather are collected in step (b) and treated subsequently in step (c).

10. The method according to any of claims 1-9, wherein sulphite rich water obtained in step (b) is recycled and reused in step (a) to partly replace the initial sulphite dosage in step (a).

11. The method according to any of claims 1-10, wherein any of the steps (b), (c) and (e), comprises further washing steps.

12. The method according to any of claims 1-11, wherein the separation steps (b) and (e) are performed by filtration.

13. The method according to any of claims 1-12, wherein the reaction temperature in step (a) is controlled at 87-90°C.

14. The method according to any of claims 1-13, wherein said sulphite ions in said first aqueous solution are from added sodium sulphite Na₂S03, sodium hydrogensulphite

NaHSC"3 or sodium metabisulphite Na₂S₂0₅.

15. The method according to any of claims 1-14, wherein the dry matter content of the feather raw material in said first aqueous solution is in the range of 5 to 15% (w/w).

16. The method according to any one of claims 1-15, wherein the feather material obtained from step (f) is subjected to enzymatic hydrolysis before the drying step (g).

17. A protein-rich modified feather product produced by the method according to any of claims 1-15.

18. The protein-rich modified feather product according to claim 17, wherein said product comprises powdered feather material having protein content more than 90% and ash content less than 1.5%.

19. The protein-rich modified feather product according to claim 18, wherein said powdered feather material has higher enzymatic hydrolysability compared to untreated feather material.

20. The protein-rich modified feather product according to any of claims 17-19, wherein said product is essentially insoluble to water.

21. The protein-rich modified feather product according to any of claims 17-20, wherein said product is not enzymically treated, preferably not protease-treated.

22. The protein-rich modified feather product according to any one of claims 17-21, wherein the content of free SH groups in said product is more than 55 μιηοΐ/g.

23. Nutritional additive comprising or consisting of the protein-rich modified feather product according to any of claims 17-22.

24. Animal feed comprising the nutritional additive of claim 23.

25. A food product comprising the nutritional additive of claim 23.

26. Cosmetic additive comprising or consisting of the protein-rich modified feather product according to any of claims 17-22.

27. A cosmetic product comprising the cosmetic additive of claim 26.

28. Packaging material additive comprising or consisting of the protein-rich modified feather product according to any of claims 17-22

29. Packaging material comprising the additive of claim 28.

30. An additive for coating or building material comprising or consisting of the protein-rich modified feather product according to any of claims 17-22.

31. The additive according to claim 30, wherein said coating or building material is cement or paint.

32. Coating or building material comprising the additive according to claim 30 or 31.

33. Use of the protein-rich modified feather product according to any of claims 17-22 as a nutritional additive, a cosmetic additive, a packaging material additive or an additive for coating or building materials.