WO2020055350A2

WO2020055350A2 - Reducing atmosphere drying

Info

Publication number: WO2020055350A2
Application number: PCT/TR2019/000038
Authority: WO
Inventors: Alvazeer Duried; Betül ÖRS
Original assignee: Iğdir Üniversi̇tesi̇
Priority date: 2018-05-11
Filing date: 2019-05-10
Publication date: 2020-03-19
Also published as: WO2020055350A3; TR201806708A2

Abstract

This invention relates to a Reducing Atmosphere Drying which can dry all biological products (dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics by preserving their chemical, sensorial and nutritional properties without using preservative chemicals by means of the circulation of gas mixture (N2 and/or C02 and/or H2) comprising reducing gas (H2) inside a dryer in the form of a closed cycle.

Description

REDUCING ATMOSPHERE DRYING

Technical Field of the Invention:

This invention relates to a new drying technique for oxygen and heat sensitive biological and non-biological products, wherein gas mixture (N2 and/or CO2 and/or H2) comprising reducing gas as drying atmosphere in order to conserve chemical, sensorial and nutritional quality parameters of all biological products (dairy products, seafood, fruit seeds, nuts and oil- rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as foods and pharmaceutics.

State of the Art:

Currently, a wide range of storage methods such as drying, canning, freezing, salting and radiation applications are utilized in the field of food preservation.

Drying is the oldest, cheapest and most common used food preservation method among those.

A majority of food products such as cereals, meat and meat products and fruits-vegetables are preserved by drying. Drying is a process which leads to a set of changes and comprises heat and mass transfer. The goal of drying is to make the product durable and stable against microbiological, chemical and enzymatic deteriorations by means of bringing moisture content of foods down to lower values, thus lowering water activity (aw) of foods under a certain value.

Even though the real goal of all food drying processes is to increase the shelf life of food, lowering the packaging, handling and storage costs of the product by reducing mass and volume of the product is among the main purposes. Thus, processing, packaging, handling and storing costs of dried food have been determined to be lower than those canned and frozen food.

The attention on dried food has greatly increased due to present life-style conditions, and recently dried food industry has taken an essential place among food industries. In addition to meet dried food demand of consumers, great amount of dried fruit production has come into question in order to prepare many products such as cornflakes, bakery products, desserts and candies at industrial sizes.

Technically, more than 500 types of dryers are stated in literature and approx. 100 types of those are used commercially. Although, a majority of different drying processes are used, conventional drying methods are the most common drying methods since they are easy to operate and are cost efficient.

Even though the drying process conserves biological products and provides many advantages, it brings along some negative drawbacks while most of these products are sensitive to drying conditions. Particularly, in conventional drying methods, it is quite rather difficult to obtain high quality product since generally high temperature during drying and oxygen-included air as drying environment are applied. Many foods such as fruits and vegetables are composed of water, carbohydrate, protein and lipid fractions and these compounds are modified easily in drying conditions where high temperatures are applied and they cause losses of food quality.

During drying, the oxygen included in the air causes browning resulting from enzymatic and non-enzymatic (Maillard) reactions in foods. Therefore, drying processes by which high temperatures and oxygen-included air as drying atmosphere when used lead to a number of negative results such as change of color pigments (carotenoids, chlorophyll etc.), oxidation of unsaturated fats and fatty acids (oleic acid, linoleic acid, alpha and beta carotene, tocopherols etc.), loss of vitamins (vitamins A, C and E, etc.), taste changes (rancid flavors in oily products) and visual deterioration.

The main reason of color changes in food is enzymatic and non-enzymatic browning (Maillard) reactions. Polyphenol oxidase (PPO) enzymes in foods such as fruits and vegetables cause enzymatic browning by catalyzing the oxidation of phenolic compounds to form brown pigment when especially when food is deteriorated or cut. Enzymatic browning occurs only by the combination of four components which are oxygen, enzyme, copper and substrate (phenolic component). Phenol components transform first into o-benzoquinones by being oxidized and then into melanin which are brown pigments during the non-enzymatic second stage.

It is estimated that more than 50% of the losses in fruit sector are caused as result of enzymatic browning. Thereby, avoiding the enzymatic browning has an essential point in this regard. PPO activity can be prevented by inactivation of the enzyme via heat, removal of one or both of the substrates (oxygen and phenols), lowering its pH to by two pH units below the optimum pH of enzyme, addition of compounds that inhibit PPO or inhibit melanin formation. The non-enzymatic browning (Maillard) reaction usually occurs in fruits containing high- level reducing sugars such as glucose, fructose and sucrose. If the moisture amount is lower than 2%, browning reaction does not occur. If the moisture amount is between 15-20%, then the Maillard reaction occurs.

The browning reactions that are not enzymatic are ongoing events continuing with a certain speed according to conditions during drying process. Enzymatic browning can be prevented by the use of chemicals such as ascorbate, sodium bisulfite, sulfur dioxide and of organic acids such as citric, ascorbic, malic and acetic acid in food industry. Sulfur dioxide and sulfides, majorly sodium sulfate, sodium bisulfate and sodium metabisulfate, have been used as chemical inhibitors of phenolase in food industry for a long time. Sulfur dioxide can be applied in the form of gas or sulfides can be applied as dilute aqueous solutions. However, their use on foodstuff may cause undesired taste and smell or may lighten the natural color of food. Furthermore, those compounds are highly toxic and have negative effects on vitamin B. Albeit having as many negative effects as mentioned, they have extensive usage area due to efficiency and low costs. There are plurality of studies showing that ascorbic acid (AA) alternatively reduces browning, whereas this acid is not suitable for use in dry products since it itself is also oxidized during drying process.

Even if browning reactions and chemical, sensorial and nutritional losses caused by these reactions by use of afore-mentioned chemicals, the demand on products containing preservatives and additives at a minimum level is increased today. Therefore, it was emphasized how to minimize preservatives in foodstuffs during drying and it was decided that obtaining high quality product depends on issues relating to equipment and technology. Even though the lyophilization process is suggested to be the best technique to obtain a higher quality product, it is not preferred due to its high operating cost.

The researchers have stated that chemical, sensorial and nutritional values of many foods such as fruits and vegetables can be maintained and their oxidative effects can be reduced in processes applied in an inert atmosphere under low oxygen conditions. In this regard, heat pump drying (HPD) technique was developed and was successfully applied to many different food types. HPD consists of two sub systems as cooling and drying systems. This technique consumes 60-70% less energy when used at the same temperature as conventional methods since it is a closed system that makes it possible to reuse the atmosphere coming out of the system (Kivevele and Huan, 2013; olak et al., 2009).

Some researcher have conducted studies by drying different foodstuffs via HPD under modified atmosphere conditions.

Ramesh et al. (1999) have stated that higher drying rate was obtained and transfers of mass and heat were performed faster by drying performed under inert atmosphere. Hawlader et al. (2006) have applied heat pump drying, vacuum and freezing drying techniques under normal and modified atmosphere (nitrogen (N2) and carbon dioxide (C02)) in order to compare 6- gingerol loss occurred in ginger with different drying techniques. As a result, they have detected that modified atmosphere increased diffusion activity compared to normal atmosphere and that 6-gingerol was contained in products dried in modified atmosphere at higher levels.

Ramesh et al. (2001) have researched the effects of nitrogen gas used for drying peppers and studied red color intensity, tocopherol, carotenoids and vitamin C as quality parameters. Santos and Silvia (2009) have determined that only vitamin C was significantly affected by atmosphere change.

Erentiirk et al. (2005) have implemented air-carbon dioxide mixture at different rates on rosehip fruit and found the highest quality on fruits dried via pure carbon dioxide. On the other hand, with the increase in oxygen concentration, the amount of vitamin C decreased and in addition to that, it was decided that the amount of vitamin C detected in the samples dried via carbon dioxide was slightly higher than those dried via nitrogen.

Perera and Rahman (1997) reported that oxidative reactions did not occur when nitrogen was used as the ambient atmosphere during the drying of food products containing sensitive compounds. Beside, C02 and N2 gases were stated to reduce browning, shrinkage and rapid rehydration. In the aforementioned works, the air of ambient atmosphere was limited to be modified with CO2 and/or N2 gases and no reducing gas (H2) was used.

Until today, hydrogen use at food industry was stated to be for margarine production industry. This way of application of hydrogen in food industry was also approved by food standards organizations as food additive in the category of propellant gas with the code E 949 (Alwazeer et al., 2003). Some published articles have suggested the use of hydrogen that is less than 4% together with nitrogen to preserve the vitamin C content in orange juice and to preserve color and antioxidant properties of dairy products enriched with polyunsaturated fatty acids during storage. (Iroux et al., 2008; Alwazeer et al., 2003)._It has been stated that the flammability level of hydrogen in the air is between the ratios of 4% to 75% (v/v), and that its explosive limits are between the ratios of 18.3% to 59% (v/v) at normal temperature and in atmosphere ambient (Najjar, 2013). It is essential to say that the stated final ratios of hydrogen are calculated over the mixture of hydrogen and air and a study formerly conducted showed that hydrogen diluted with nitrogen reduced the normalized mass combustion rate and the flammability index and thus the risk of hydrogen explosion (Tang et ah, 2009). That is to say, the dilution of hydrogen with nitrogen (as done in our patent) reduces the risk of explosion.

The patent application CN201392011 describes "Special food drying heat pump assembly". This system comprises an evaporator, a R134A compressor, a condenser and an expansion valve.

The patent application CN202648346 describes "Heat pump drying system". This heat pump drying system comprises a heat supply system, a heat utilization system and a control system. The control system comprises a compressor, a condenser, an evaporator, a reversing valve and a throttling device. It can be applied to a plurality of industries such as medicine, food and agriculture, and is high energy-saving, environment friendly and has intelligent temperature regulation feature.

The patent application CN107238276 describes "Mobile, medium-low-temperature heat pump drying system". This system comprises a heat pump unit, a frequency-conversion axial-flow fan and a circulating fan. The heat pump unit is composed of a compressor, an evaporator, a condenser, an auxiliary condenser, a by-pass valve, an expansion valve, a drying filter and a liquid storage tank; the circulating fan is located between the heat pump unit condenser and the evaporator; and the frequency-conversion axial-flow fan is installed on the auxiliary condenser and is used for assisting in forced convection heat dissipation of the auxiliary condenser. This drying system can be suitable for food drying and other drying production processes with the same dying process and similar drying conditions.

The patent application 2015/12570 describes "Closed cycle modified atmosphere dryer (KADMAK)". That invention relates to a furnace capable of performing Drying in the Closed Cycle Modified Atmosphere which ensures that fruit, vegetable etc. foodstuffs sensitive particularly to oxidative drying are transformed into a product which is in good quality and is nutritious by lowering their moisture amount to desired level without using additives.

Definition of the Invention:

Our invention is a drying technique which minimizes the disadvantages of conventional drying techniques, and which can be used on all biological products (dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics, characterized in that it is a drying technique which uses a gas mixture (N and/or CCh and/or H2) comprising reducing gas (H2) as drying atmosphere, and is formed of a closed system, and has high energy efficiency, and is cost efficient and makes it possible to produce high quality dry product.

By the invention, the oxygen present both in the product and also in drying atmosphere is neutralized beside other oxidants such as free radicals, and drying process becomes more efficient than formerly studied nitrogen (N2) and carbon dioxide (CO2) gases. Thus, chemical, sensorial and nutritional losses such as change of color pigments (carotenoids, chlorophyll etc.), oxidation of unsaturated fats and fatty acids (oleic acid, linoleic acid, alpha and beta carotene, tocopherols etc.), loss of vitamins (vitamins A, C and E, etc.), taste changes (rancid flavors in oily products) caused by oxygen, free radicals and other oxidants are minimized and high quality product is obtained in accordance with desire of the consumers.

Since the system used by the present invention is closed, drying atmosphere is circulated inside the system and the gas mixture is not continuously supplied to the system but at certain intervals. Thereby, the energy efficiency is higher when compared to conventional methods.

While the system comprises a moisture separator and a gradual condenser system, the moisture transferring from the product to drying atmosphere is much more rapidly absorbed and the drying process is performed faster when the moisture load on drying atmosphere is reduced.

Apricot and apple fruits were dried by the Reducing Atmosphere Drying which is subject matter of the present invention, and the change occurred on the color of product dried by reducing atmosphere drying was evaluated by comparing to fruits dried by different drying methods such as hot-air oven, freeze-drying and vacuum drying.

Object of the Invention:

The object of the invention is to minimize chemical, sensorial and nutritional losses occurred during drying process on all biological products (dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics by use of a gas mixture comprising reducing gas instead of normal air as drying atmosphere. By means of using reducing gas contained in drying atmosphere, more efficient results than formerly studied nitrogen (N2) and carbon dioxide (CO2) gases are obtained as oxygen, free radicals and other oxidants included in ambient and products are minimized.

Another object of the invention is to avoid color losses caused by browning reactions occurred on biological products without utilizing preservatives negatively affecting the health such as sulfur compounds.

A further object of the invention is to enhance energy efficiency by supplying the gas mixture to the system at certain time intervals instead of supplying it continuously owing to the fact that the dryer is developed as a closed system.

Description of the Figures:

Fig. 1: Diagram of reducing atmosphere drying system

Fig. 2 : Side view of the drying cabin

Fig. 3 : Front view of the drying cabin and the structure of drying tray

Description of the References in the Figures

1: Nitrogen (N2), carbon dioxide (CO2) and hydrogen (Ffr) gas ylinders

2: Gas mixer

3: Gas circulator

4: Heater

5: Drying cabin

6: Moisture separator / gas flow indicator

7: Gradual condenser system 8: Drying tray 9: Gas inlet

10: Gas outlet

Detailed Description of the Invention:

The invention relates to a new drying technique for oxygen and heat sensitive biological and non-biological products, wherein gas mixture (N2 and/or CO2 and/or H2) comprising reducing gas as drying atmosphere in order to conserve chemical, sensory and nutritional quality parameters of all biological products (dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics.

The invention is a closed drying system comprised of nitrogen (N2), carbon dioxide (CO2) and hydrogen (H2) gas cylinders (1) which are the source of drying atmosphere, a gas mixer (2) in which the gases are mixed, a gas circulator (3) enabling the gas flow cycle in the system, a heater (4) heating the gas circulated in the system, a drying cabin (5) comprising the product to be dried and a moisture separator (6) in which the moisture in the system is firstly absorbed and which serve also as gas flow indicator, a gradual condenser system (7) condensing the unabsorbed moisture remained in the drying atmosphere and a grid-like drying tray (8) located in the drying cabin, and on which the product to be dried is placed. The gas mixture (Nitrogen (N2) and/or carbon dioxide (CO2) and/or hydrogen (H2)) to be introduced to the system is set via gas mixer (2) and the obtained gas mixture is sent to the heater (4) by the gas circulator (3). The gas mixture set to desired temperature in the heater is transferred to the drying cabin

(5) that is heat and light isolated and comprising the grill-like drying tray (8) on which the product is placed.

The reason why the drying tray (8) on which the product is placed for drying is in the form of a grid is that it is desired to perform the drying more uniformly. When the gas mixture reaches the moisture separator (6) which is made of silica gel, some part of moisture is retained here and some is condensed in the gradual condenser system (7) and the moisture load of the drying atmosphere is reduced and the drying time is shortened.

While the invention is made of a closed system, the gas mixture output from the gradual condenser system is supplied back to gas circulator (3) again. Although the gas mixture circulated inside the system is repeatedly used, fresh gas mixture is needed to be supplied to the system at certain time intervals.

When the gas flow is supplied to the system, the silica gel inside the moisture separator system

(6) is moving and the speed of this movement is used as the gas flow indicator.

Applicability in Industry:

The invention relates to a new drying technique for oxygen and heat sensitive biological and non-biological products, wherein gas mixture (N2 and/or CO2 and/or H2) comprising reducing gas as drying atmosphere in order to preserve chemical, sensorial and nutritional quality parameters of all biological products and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics, wherein, by means of minimizing oxygen, free radicals and other oxidants included in ambient or in the products, more efficient results than formerly studied nitrogen (N2) and carbon dioxide (CO2) gases are obtained, color losses caused by browning reactions occurred on biological products are avoided without utilizing preservatives negatively affecting the health such as sulfur compounds, energy efficiency is enhanced by supplying the gas mixture to the system at certain time intervals instead of supplying it continuously owing to the fact that the dryer is developed as a closed system.

It can be used for dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant -rich materials such as spices and aroma-rich products and raw materials and for non- biological products.

It is preferable in food industry due to those advantages it brings.

Claims

1. This invention is a Reducing Atmosphere Drying System in which a gas mixture comprising reducing gas (fh) for drying all biological products (dairy products, seafood, fruit seeds, nuts and oil-rich products such as olives, roses and tea leaves, fruits and vegetables, medicinal and aromatic plants, antioxidant-rich materials such as spices and aroma-rich products and raw materials etc.) and non-biological products which are oxygen and heat sensitive such as food and pharmaceutics, characterized in that it comprises;

- Nitrogen (N2) and/or carbon dioxide (CO2) and/or hydrogen (H2)) gases (1) which are source of the gas mixture,

- A gas mixer (2) mixing the gases in certain proportions,

- A gas circulator (3) that provides gas circulation in closed system,

A heater (4) bringing the gas mixture to desired temperature,

A drying cabin (5)

A grill-like drying tray (8) located inside the drying cabin and on which the products are placed for drying,

- A moisture separator (6) where moisture transferring from product to the gas

mixture that is drying atmosphere is firstly absorbed,

A gradual condenser system (7) which is the portion where the moisture released from product is condensed.

2. The Reducing Atmosphere Drying System according to Claim 1, characterized in that; it is a closed system which ensures that product is dried by heating the gas mixture (N2 and/or CO2 and/or H2) comprising reducing gas obtained by the gas mixer (2), and by transferring it over the product located in the drying cabin (5) to the systems, where the moisture is separated, via the gas circulator (3).

3. The Reducing Atmosphere Drying System according to Claim 1, characterized in that; it comprises the drying cabin (5) having a tray on which the product is placed for being dried.

4. The Reducing Atmosphere Drying System according to Claim 1, characterized in that; it comprises the drying tray (8) allowing the product to be dried uniformly owing to its grill-like holes.

5. The Reducing Atmosphere Drying System according to Claim 1, characterized in that; it comprises the moisture separator (6) which is capable of separate the moisture transferred from product to the gas mixture, and which contains silica gel that is reusable by being kept 2 hours at 120 °C degrees after absorbing moisture at a maximum level of its capacity.

6. The Reducing Atmosphere Drying System of Claim 1, characterized in that; it comprises the gradual condenser system (7) which is capable of condensing the moisture of the gas mixture, taken from the dried product, by using negative temperatures (freezing) and which can reduce moisture load of the gas mixture.