CA1062538A - Coating of potatoes to prevent greening - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method for preventing greening due to chloro-phyll formation in raw unpeeled potato tubers exposed to light prior to and including retail sale which comprises spraying or dipping the tubers in an aqueous emulsion containing a surfactant so as to form a continuous film on the surface of the tuber which is relatively impermeable to carbon dioxide thereby ensuring an atmosphere containing at least 15% CO2 within the film and in the tuber. The surfactant preferably contains long chain fatty acid moieties and polyoxyalkylene or polyhydroxy moieties, and has an HLB
rating below about 15. The amount of surfactant required can be substantially reduced and a tighter film produced by addition of an aliphatic hydroxy acid containing 3-6 carbon atoms to the surfactant emulsion before application.

Description

~o62s38 COATING OF POTP.TOES TO PREVENT GRE:ENING
This invention relates to the treatment of raw, unpeeled potato tubers to prevent greening thercof.
Many varieties of pot~toes green rapidly when exposed to light and this has become a major problem in marketing potatoes in "see-through" plastic bags in super-markets. Even exposure to light intensities as low as 100 foot-candles for as little as 24 hours can cause greening in potatoes. Such light intensities are frequently attained by the fluroescent lighting commonly employed in supermarkets. Such exposures not only cause greening, which has been shown to be due to chlorophyll formation, but also cause bitterness and off-flavour.
Bitterness and off-flavour are believed to be due to an excess of the alkaloid, solanine. Ingestion of green potatoes containing large amounts of solanine may cause severe illness and, occasionalLy, death in man.
Traditionally, therefore, green potatoes are rejected by the consumer who, at the same time wishes to see what he or she is buying and demands the use of transparent packaging materials.
Many compositions and methods for overcoming the problem of greening have been suggested. ~or example, the use of controlled special atmospheres either in bulk or in gas tight sale containers or bags is suggested in United States Patent 3,533,810 but is acknowledged to be unduly expensive and cumbcrsome, furthermore moisture accumu-B lat~ons in the bags is considered unsightly. Similarly, the use of specially coloured fluroescent lights ~e.g.
green and gold) has been proposed but has only limited effectivcncss and applicability. Hot wax dipping with

- 2 -ra/

and without the addition of minor amounts of surfactant to aid wetting has been proposed in United States Patent 2,755,189 and in other references but, although effective, is expensive and suffers from the disadvantage that the wax is relatively difficult to remove without damaging the 6kin of the potato thus severely limiting the manner in which the potato may be prepared for table use. Wu et al (J. Amer. Soc. Hort. Sci. 97(5) 614-616, 1972) have sug-gested that the problem may be overcome by dipping the potato tubers in coxn oil, such as that sola under the trade mark "MAZOLA", but this i~ relatively expensive, may result in suffocation of the tuber and furthermore limits the way in which the tubers may be cooked as the oil cannot be easily B removed without removing the epidermal layer~ or skin of the tuber. United ~tates Patent 3,051,578 suggests treating potatoes with a diluent containing ethylene-diamine tetra-acetic acid (EDTA) or its calcium, sodium or potassium salts.
However, because of the sequestering action of EDTA on calcium, only a verv limited use of the calcium salt only of EDTA is permitted for use in foods in at least some countries in-cluding Canada where this invention was made. Neither EDTA
nor any of its salts can be applied to raw agricultural foodstuffs in certain countries including Canada, and hence the method-is clearly impractical.
It is, therefore, an object of the present invention to provide a cheap, simple, safc and effective method for treating potatoes to prevent greening due to the production of chlorophyll when the potatoes are removed from cold ~torage and before thcy are sold at the retail level.

3~ Is has bcen found that chlorophyll production can bc substantially completely inhibited in an atmosphere con-lx/~ ~
., , . , _, 106253~

taining at ledst 15~ CO2 but as noted heroinabove it has bcen been found gencrally impractical to provide an external CO2 atmosphere. ~e have discovered that an internal C02 atmos-phere within the potato tubers is equally effective. It has been found that for a period of about 48 hours after removal from cold storage, potato tubers undergo a burst of aerobic respiratory activity which generates carbon dioxide. ThP problem then is to provide a suitable film around the tuber which is relatively impermeable to CO2 so as to cause CO2 to accumulate within the tuber by aerobic respiration so that the concentration near the potato surface will be controlled at the minimum concentration required to prevent greening, generally considered to be about 15%. The film must also be capable of uniform application and rela*ive-ly permeable to oxygen in order to preclude the development of anaerobiosis or smothering over the range of temperatures encountered from low temperature storage to retailing. The film material must also be transparent and edible as it may not be removed prior to preparation for table use.
We have found that suitable film forming materials may be selected from long chain fatty acid derivatives commonly used as surfactants. In particular, we have found that slight-ly lipophilic to moderately hydrophillic polyoxyethylene sor-bitan fatty acid esters, sorbitan fatty acid esters and poly-ethylene glycol fatty acid esters are suitable. All of the above surfactants are presently used by food processors, and may also be applied to foodstuffs in pesticide formulations and post harvest treatments. Their use is not monitored on raw agricultural products and they are therefore believed to be acceptable additives by Federal Regulatory ~uthorities.
Thus, by one aspect of the present invention there is ~4 lr/~

provided a me~.hod for treating raw unpeeled potato tubers to inhibit greening due to chlorophyll dovelopment comprising applying an emulsion consisting essentially of a surfactant and water to said tubers in a quantity sufficient to fo~m a thin oontin-uous film of said surfactant thereon and drying thereon;
said surfactant containing long chain fatty acid moieties and polyoxyalkylene or polyhydroxy moieties and having an HLB below about 15.
The invention will now be described in more detail with reference to the following drawings in which:
Fig. 1 is a graph showing development of chlorophyll under elevated CO2 and normal 2 concentrations in peel re-moved from Xennebec tubers 48 hours earlier and exposed to laboratory temperatures (24-27C) and minimum bench level illumination of 1076 lx.
Fig. 2 is a graph showing development of chlorophyll under reduced 2 in peel removed from Kennebec tubers 48 hours earlier and exposed to laboratory temperatures t24-27C) and minimum bench level illumination of 076 lx.
Fig. 3 is a graph showing respiration measured at 21C
in Kennebec tubers in the interval following withdrawal from 5C storage. Tubers were sprayed to runoff with Tween 85 and retained in light at laboratory temperatures (24-27C).
~ig. 4 is a graph-showing internal CO2 and 2 concentra-tions in potato tubers (numbered clone) sprayed to runoff with various concentrations of Tween 85 immediately following with-drawal from 5C storage and measured after 5 days at laboratory temperaturcs (24-25C); and Fig. 5 is a graph showing changes in internal CO2 and 2 concentrations in Kennebec tubers sprayed to runoff with 4% Tween 85 immediately after withdrawal from 5C storage.
~s previously noted, the film ~orming materials lx//.. '1 found suitable to resist the oxodus o CO2 from the potato tubers are generally long chain fatty acid esters or glycerides which are relatively common sur-factants. We have found that the series of polyoxyethylene sorbitan fatty acid esters sold under the Registered Trade Mark TW~EN by Atlas Chemical Corp. are generally suitable and TWEEN 85 in particular. Similarly, the series of sorbitan fatty acid esters sold under the Registered Trade Mark SPAN by Atlas Chemical Corp.
are generally suitable. Polyethylene glycol fatty acid esters selected from those sold under the Registered Trade Mark PEGOSPERSE may also be suitable.
In order to illustrate the present invention a series of experiments was conducted.
Example I
Tubers from cvs, Avon, Fundy, Keswick and Kennebec and a numbered clone were used. Because Kennebec greened most readily it was used most often. Whole tubers, previously stored in darkness at 5C, were exposed to laboratory temperatures of 2Io-27oc and to a minimun illum-ination at the bench level of 1076 lx (cool white fluroescent) on a continuous basis. When required, discs of peel tissue were cut with a No. 6 stainless cork borer and excised at a depth of 0.16 cms with a stainless steel knife.
Chlorophyll in potato discs was estimated visually and by the method of Arnon (Plan.t Physiol. 24,1-15, 1949) using a Beckman DB spectrophotomcter and 5 discs (0.75 g) per sample.
CO~ and 2 were determined with a Fry analyser whose calibrated capacity WAS matched with a 1 ml all glass 6yringe. Internal gases from tubers were sampled using a ~ * trademark r~ - 6 _ ~062538 quick evacuation technique. This technique utilizes the purging action of steam at prevailing atmospheric pressure, and the subse~uent vacuum formed after the ~ystem is sealed and the steam condensed.
~ espiratory CO2 was determined with the aid of a Beckman infra-red gas analyser.
Discs sampled from treated and untreated potatoes were variously exposed to air and to concentra-tions of CO2, 2 and balance N2, by placing them on moistened Whatman No. 3 filters in open glass dishes;
- tissues and dishes were contained in humid environments inside wide mouthed glass preserving jars of 3640 ml capacity.
The tubers were sprayed to the point of runoff with an aqu~ous emulsion formulated with Tween 60 (poly-oxyethylene (20) sorbitan monostearate) or Tween 85 (polyoxyethylene (20) sorbitan trioleate). All applica-tions were made immediately after withdrawal of the tubers from storage.
RESULTS
Anti-greening treatments: The amount of material required to control greening varied substantially with the cv (Tables 1 & 2). A 15% emulsion of Tween 60 con-trolled greening in the susceptible Kennebec cv. On a weight of material applied basis, Tween 85 was the most eficient substance; a residual of 0.40 g/kg of tuber, applied by spraying to runoff with a 5% emulsion was generally more than required. Control of greening was largely assessed by visual means and was considered more ~han adequate if chlorophyll did not exceed 0.40 mg/100 g peel.

Ir/" ~

C2' 2~ and greening in exciscd peel: When discs from control tubers were retained in atmosphercs containing high concentrations of CO2 (and 20~ 2 balance N2), chlorophyll development decreased with increased CO2 concentration (Fig. l). However, concentrations as high as 40% allowed some chlorophyll formation. When discs were retained in atmospheres of reduced 2 (and 0.0~ CO2, balance N2), there was no inhibition of chlorophyll formation until 2 concentrations were reduced below 5%
(Fig. 2). When discs were retained in atmospheres of increasing CO2 concentrations with the 2 fixed at a slightly reduced level (15~), and balance in N2 the results closely resembled those of Fig. l.
C2 output from tubers treated with Tween 85: Tween 8S
suppressed or dPlayed the norma~ respirational "burst"
which results when the tuber is removed from low tempera-ture storage to higher temperatures (Fig. 3) but tended to sustain the CO2 output at higher levels when compared with controls over the whole period of observation (15 days approx.). Ultimately respiration declined sharply toward the control level.
Internal CO2 and 2 in tubers treated with Tween 85: The . . .
concentration of the applied surfactant, and thus pre-sumably its weight, had a direct influence on the accumula-tion of internal CO2 and the decline in internal 2 (Fig. 4).
In this instance a concentration of 4% Tween 85, which was sufficient to control grecning, produced average internal concentrations of 17% CO~ and 16% 2 (approx.) 5 days after ~reatment. Th~ pronounced accumulating effect of 4~ Tween 85 on internal CO2 in ~ennebec tubers is seen in Fig. 5.

Althou~h both CO2 and 2 concentrations began to return to lr/,-~

106Z53~3 .

T nL~ 1 Grc~n color devclopment in potato tubers trcated with aqueous emulsions of Tween G0 and rRtained at laboratory tem~erature~ (29-27C) under a minimum of 107G lx fluorescent light (CW) .. .. . _ .
Chlorophyll (mg/100 g peel) Kennebeca Avon~ Ke6wic~;b Control (water) 6.75 3.67 4.44 5~ Tween 60 8.08 0.28 1.11 10~ Tween 60 3~31 0.08 0.39 15% Tween 60 0.31 - -Initial color . 0.07 0.05 . 0.06 - . .. . _ - '. .
a After 13 days b After 36 days Greening assessment in potato tubers treated with aqueous emuisions of Tween 85 a~n~ retained at laboratory ~- temperature (24~27C) under a mi`n1mu~ of 1076 lx .fluorescent light (CW) ~ w~
I .. IL3 - .. . . . . ..
Greening - after 6 days ~ ween-85 . ~~~
Yariety. 0-.-0 2.S ~ 5.0 -:7.S
. _ . _ .. . _ ... _ . , . . _ .
Avon Keswick +- - - ~
Fundy +
Kennebec~+ +-Greening - after 13 days ~von ~ +-Ke~wick + +-~undy ++ ~ _ ~
Kennebec~+~+ +~ - -.

~06Z538 normal 6 days after treatment, CO2 concontxations still d~fered sharply from thc controls after 16 days.

Other observations: In some instances both Tween 60 and Tween 85 were applied to tubers at substantially higher concentrations than were required to stop green-ing. Tween 60 at 20%, and Tween 85 at 7.5% produced glossy surfaces (an apparent film) which persisted for several hours and even days. Vnder these conditions internal CO2 approached 100% (>90%) and internal 2 approached zero (<1.5~) and some tubers suffocated. When these glossy suraces were abraded, (or punctured), thus removing both surfactant and epidermal layers, greening developed in the area proximal to the abrasion.

Example 2 The experiments described in Example 1 were repeated the following season using a more comprehensive collect;on of Tweens. Kennebec tubers were again sprayed to runoff, but dips in warmed emulsions were used to apply Tween 61 (65.6C) and Tween 65 (40.6C). Visual assessment was relied on to determine the presence or absence of greening. Chlorophyll concentrations were determined in tubers treated at surfactant concentrations proximal to the "optimum" using the method of ~rnon ~ibid), 0.75 g of peel, and a Beckman Model DB spectrophotometer;
in greened potatoes, tissues lr/" ,~

~o6Z538 were ~elected from thc greenest areas. Greening was observed to occur when determinations exceeded 0.85 mg/75 g peel.
When compared with previous observations, the figures in Table 3 indicated an increased effectiveness With Tweens 20, 80, and 60, while that of Tween 8S
remained unchanged.
Using linear interpolation, the weights of sur-factant applied at the concentrations listed in Table 3, and the figure 0.85 mentioned above, the weight rate of each surfactant required to control greening was calcu-lated and is listed in Table 4. It is readily apparent that Tweens vary widely in their relative efficacy, and that efficacy in terms of concentration does not necessarily relate to efficacy in terms of mass applied.
Example 3 ~ old stored (5C) cv Kennebec tubers were sprayed with aa,ueous emulsions of mixtures of Tween and Span and then exposed to continuous fluorescent illumin-B ation k~s 1076 lx) for 15 days. The resul~s are tabulated in Table 5.
- -Example 4 Cold stored Kennebec tubers were sprayed with various PEGOSPERSE surfactants and exposed to fluorescent light as in Example 3. The weight of surfactant required to control greening for the different surfactants is tabulated in Table 6.

106;~538 TAB~E 3 Tween surfactants in aqueous emulsion ranked for greening control in Kennebcc tubcrs. Tubers were treated on removal from 5C storage, retained 15 days at laboratory temperature (21 ~ C) under continuous fluorescent illumination re~ 1076 lx).

Reduced greening Zero qreening Rank ~lghest conc. Chlorophyll Lowest conc.
- tested (%) % of control . tested (%) 1. Tween 81 2.0 17.3 3.0 2. Tween 65 2.0 81.3 4.0 3. Tween 85 4.0 27.9 5.0

4. Tween 61 4.0 26.4 6.0

5. Tween 60 4-0 65.0 6.0

6. Tween 80 - 10.0 16.' 12.0

7. Tween 21 9 0 28.9 12.0

8. Tween 40 12.0 18.0 15.0

9. Tween 20 12.0 59.8 16.0 .... . .. . . _ . .
P.O.E. (No.) - Number of polyoxyethylene units Tween 81 - P.O.E. (5) sorbitan monooleate Tween 85 - P.O.E. (20) " trioleate Tween 80 - P.O.E. (20) " monooleate Tween 61 - P.O.E. (4) " monostearate Tween 65 - P.O.E. (20) " tristearate Tween 60 - P.O.E. (20) " monostcarate Tween 40 - P.O.E. (20) " monoplamitate Tween 21 - P.O.E. (~) " monolaurate Tween 20 - P.O.E. (20) " monolaurate Span 20 - P.O.E. (0) " monolaurate lr/~

T~LE 4 The weight of various Tween surfactants requirçd to be applied eithcr as an aqueous spray or dip to control greening in Kcnnebec tubers subscquently cxposed for 15 days to continuous fluorescent light (cw 1076 lx) . at laboratory temperatures (21-27C?

.
Surfactant of tubérs .
1. Tween 81 - P.O.E. ~5) sorbitan monooleate 0.15 2. Tween 85 - P.O.E. (20) " trioleate 0.23 3. Tween 60 - P.O.E. (20) " monostearate 0.27 4. Tween 80 ~ P.O.E. (20) " monooleate 0.44 5. Tween 40 - P.O.E. (20) I- monopalmitate 0.71 - 6. Tween 65 - P.O.E. (20) " tristearate 0.83 7. Tween 61 - P.O.E. (4) " mono- ** 0.94 8. Tween 20 - P.O.E. (20) " mono~a~ra~ee 0.98 9. Tween 21 - P.O.E. (4) " monolaurate 1.32 .
P.O.E. (No.) - Number of polyoxyethylene units Applied as a dip at 40.6C.
Applied as a dip at 65.6C.

Chlorophyll development in cold-stored Kennebec tubers (5 C) after 15 days cxposure at laboratory temperatures ~21-27C) to continuous fluoresccnt illumination (CW
1076 lx). Some tubers were sprayed with aqueous emulsions of Tween and Span prepared in 1:1 ratios by weight.
~eadings <0.85 mg indicate no chlorophyll development _ * Chlorophyll (mg/75 g peel) Tween :
- Span Tw 2 0 Tw 4 0 Tw 60 Tw 65 Tw 8 0 Tw 8 5 conc (~) Sp 20 Sp 40 Sp 60 Sp 65 Sp 80 Sp 85 .
- 6.0:6.0 0.18+.04 5.0:5.0 0.15+.05 4.0:4.0 0.67+.03 2.50+.01 0.16+.00 3.0:3.0 1.74+.09 4.14+.08 2.81+.07 2.5 2.-5 0.45+.0~ 0.93+.05 2.0:2.0 2.61+.05 0.75+.08 0.29+.12 O 4.04+.22 5.29+.73 6.54+.04 4.05+.23 6.54+.0a 5.29+.73 Tween 20 - polyoxyethylene (20) sorbitan monolaurate Tween 40 - " " " monopalmitate Tween 60 - " " " monostearate Tween 65 - " " " tristearate Tween 80 - " " " monooleate Tween 85 _ n ~ trioleate Span (no) - consists of corresponding Tween molecule without-polyoxyethylene units, i.e., Span 20 - sorbitan monolaurate.
TABL~ 6 The weight of various Pegosperse surfactants applied as aqueous sprays to control greening on cold-stored (5C) Kennebec tubers subsequently exposed for 15 days to con-tinuous fluorescent light (CW 1076 lx) at laboratory temperatures (21-27C).
Wt/kg Surfactant of tubers .
1. polyethylene glycol (400) ditri ricinoleate 0.15 g 2 . n H ~I dilaurate 0.20 g 3 ~ H ~ monotallatc 0. 24 g 4 . n n ~ dioleatc 0.36 g 5. ~ H (200) monolauratc 0.56 ~
6. n H , n dilaurate 0-75 g ra/ B 14-From the above experimental results w~ have determined that greening control depcnds, at least to some extent, upon the molocular structure of the surfac-tant added and it is believed that the following generalizations hold:
Comparing Tweens 81, 85, 80 -~hortening POE
increasing fatty acid ) beneficial substitution LO Comparing Tweens 65, 61, 60 -shortening POE
increasing fatty acid ) beneficial substitution Comparing Tweens 20, 21 -shortening POE ) beneficial Comparing the fatty acid substitutions beneficial effects may be ranked: tristearate > trioleate > monostearate > monooleate > monopalmitate > monolaurate.
Thus, it is believed that ef~ec':iveness in greening control is related to the HLB (Hydrophile-Lipophile Balance) rating of the surfactant used. The HLB rating of a surfactant is a well-known method of assigning a numerical value to surfactants to provide a classification based upon their behaviour and solubility in water. Essentially the HLB rating is a function of the ~leight percentage of the hydrophilic portion of the molecule of a non-ionic surfactant. The experimental procedure to determine HLB
values is long and tedious but has been described in detail in the literature (J. Soc. Cosmetic Chem. I, 311-326, 1949), and eomparative ranking lists have been published by Griffin in J. Soc. Cosmetic Chcm. V, No. 4, p.249, Dec.,1954.
Reprosentative surfactants examined for use in tho prcsent invontion have liLB ratings (as listed in Tho _ 15 -r~/

Amer~can Perfumer and Essential Oil Review, Vol. 65, No. S, p.27-29, May, 1955) as follows:
T~BLE 7 . . .

Surfactant Chemical DesignationHLB Rating (+l) .. .. ...
Span 85 Sorbitan trioleate 1.8 Span 65 Sorbitan tristearate 2.1 Span 80 Sorbitan monooleate 4.3 Span 60 Sorbitan monostearate4.7 Span 20 Sorbitan monolaurate 8.6 Tween 81 Polyoxyethylene sorbitan monooleate 10.0 Tween 65 Polyoxyethylene sorbitan tristearate10.3 Tween 85 Polyoxyethylene sorbitan trioleate 11.0 Tween 60 Polyoxyethylene sorbitan monostearate14.9 Tween 80 Polyoxyethylene sorbitan monooleate 15.0 Tween 40 Polyoxyethylene sorbitan monopalmitate 15.6 Tween 20 Polyoxyethylene sorbitan monolaurate16.7 _ . . _ . .
From a consideration of the molecular structure of the surfactants outlined above in relation to the test results reported in Examples 1-4, we have determined that - for effective and economical control of greening in susceptible potato tubers, surfactants having an HLB rating below about 15 are most suitable. Preferably, a surfactant having an HLB rating in the range between about 8.6-11.0 should be employed. Above HLB 11, the amount of surfactant required for effective control may become excessive in some potato varieties.
In a modified process according to the present invention we have found that when the escape of respirational C2 is impeded and thus cau.sed to accumulate within the potato rA/ - 16 -tuber tissue, the acids participating in the respiration (TCA
cycle acids) may accumulate, or their rate of consumption may be reduced. Additionally, other plant acids may also accumulate.
Thus, potato tuber tissues experiencing anaerobic conditions are known to accumulate lactic acid and applicants have, in fact, observed an increase in hydrogen ion concentration (pH 6 to pH 3.5 approx.) in tubers treated with effective concentrations of surfactant. Further, the presence of mild acids in plant tissues is known to cause a proton shift reducing chlorophyll to brown pheophytin. However, when acid is applied externally in a non-phytotoxic manner, new chlorophyll develops upon exposure of the tuber to light, as soon as the applied acid is-metabolized or diluted. But, if the escaping respirational C2 is restricted slightly with a "small" amount of surfactant (that is less than what is required to control greening), the applied acid may be caused to persist for a few days, thus precluding the redevelopment of chlorophyll for a few days.
This effect however can be greatly reinforced by a "tightening"
of the surfactant film applied to the tuber which is caused by the addition of certain plant acids. These plant acids may be added to the aqueous surfactant emulsion at the time of preparation and appear to be compatible (soluble in emulsion) with the surfactant. Thus, the amount of surfactant required to produce an effective film upon application to the tuber may be reduced far below the concentration required for control of greening by the surfactant alone, and by the addition of increasing amounts of the selected acid can be rendered sufficiently impermeable to CO2. Effective combinations of surfactant and selected acid are many, and permit attenuation of the safe and effective concentration ranges.

Examples of acids which are effective in "tightening"

ra/ - 17 -1~)62538 the surfactant films, are enumerated in Table 8. An indication of their relative performance is shown in Tables 9,

10 and 11.

The relative inhibitory effect on greening in Kennebec tubers sprayed to run-off with aqueous emulsions of Tween 60 combined with various plant acids. Tubers were sprayed upon removal from 3.3C storage and retained at 22.2C under fluorescent illumination (1076 lx).
.
. .
Treatment Days before greening . . . _ . _ . . _ 1. Water only 2. 2% Tween 60 3. 2% Tw 60 + 7.5~6 lactic ac. 3 4. 2% Tw 60 + 15% lactic ac. 5 5. 2% Tw 60 + 596 ascorbic ac. 3 ~ 6. 2~6 Tw 60 + 109~ ascorbic-ac. - 4 7. 2% Tw 60 + 7.5~6 tartaric c-c. 3-6 8. 2% TW 60 + 15% tartaric ac. 5-8 9. 2% Tw 60 + 596 D-isoascorbic ac. 3 10. 2% Tw 60 + 10% D-isoascorbic ac. 8 plus

11. 2% Tw 60 + 5% citric ac. 17 plus . .

Internal CO and O in Kennebec tubers treated with (i) wa~er onl~ - controls (ii) Tween 60 (iii) Tween 60 plus citric acid, upon removal from 3.3C storage and retained for various intervals at 22.2C under fluorescent illumination (CW-1076 lx).
.
.
Day Treatment *~ C2 2 C2 2 2 2 2 2 .
Control 3.5 19.5 2.619.5 4.1 l9.S2.3 18.8 2% Tween 60 3.5 19.53. 719.0 3.519.~ 2.5 19.0 2% Tw 60 + 5% citric ac. 3.5l9.S 7.8 18.412.7 17.6 lS.S 16.3 2% Tw 60 + 10% citric ac. 3.5 19.5 9.518.516.7 lS.925.1 15.2 _ _ . . . _ . . .
* % C2 and % 2 measurement~ entered under day 3 and 5 actually made on day 2 and 4 respectively ra/ - 18 -~062538 TAsLE 10 Respiration of Kennebec tubers in the interval following withdrawal from 3.3C
storage when retained at 21C and under fluorescent illumination of 1076 lx. Tubers were sprayed immediately upon removal from storage with (i) water (controls), (ii) 2% Tween 60, (iii) 2% Tween 60 plus 7.5% lactic acid, . (iv) 2% Tween 60 plus 15% lactic acid, (v) 2% Tween 60 plus 7.5% tartaric acid, (vi) 2% Tween 60 plus 15~ tartaric acid.
.

Respiration rates (ml C0 ~ gtissue/hr) 2% Tw 60+2% Tw 60+ 2% Tw 60+ 2% Tw 60+
Day Control2% Tw 60 7.5% lactic 15% lactic 7.5% tartaric 15%
tartaric 0 5.0 1 15.9 11.5 5.3 3.1 1.9 1.7 2 17.3 13.5 7.9 6.2 3.5 3.3 3 lS.l 13.2 8.6 7.1 4.5 4.6 8 6.4 7.2 8.1 7.2 6.8 6.8 20 9 5.5 6.2 7.0 6.7 6.5 6.5 5.4 6.0 6.9 6.7 7.7 6.8 13 4.3 4.3 5.3 5.9 7.4 7.0 Respiration of Kennebec tubers in the interval following withdrawal from 3.3C storage when re-tained at 21C and under fluorescent illumination of 1076 lx. Tubers were sprayed immediately upon removal from storage with (i) water (controls), (ii) 2~ Tween 60, (iii) 2~ Tween 60 plus 5% citric acid, (iv) 2% Tween 60 plus 10~6 citric acid, (v) 2~ Tween 60 plus 15% citric acid.

Respiration rates (ml CO~cg tissue/hr) 2% Tw 60+ 2% Tw 60+2% Tw 60+
Day Control2% Tw 605% citrie ac.10% eitric ac. 15% citric ac.
0 6.7 1 18.4 11.2 2.2 1.9 1.4 2 17.0 11.8 3.3 2.6 1.7 3 15.2 13.2 6.6 5.3 4.4 4 10.5 10.7 6.6 5.8 5.2 40 7 6.6 7.4 7.7 6.8 8.6 9 6.3 6.0 8.5 8.6 13.0 6.7 5.7 9.7 9.2 13.3 11 5.7 5.0 9.4 9.5 11.9 14 5.6 3.8 10.0 16 6.4 4.6 12.1 12.4 12.2 17 7.0 4.7 13.3 13.6 12.8 .

B ra/ - 19 -Similar tests have also been conducted with Tween 81 and Tween 80, with substantially similar results.
Table 9, which is a similar and analogous compilation of data to that shown in Figs. 4 and 5, clearly shows the effect that adding certain acids to an aqueous surfactant emulsion ~or solution) has on the build-up of internal CO2, so essential to the control of greening in this process, within the tuber. This physical phenomenon can also be appreciated by examining Tables 10 and 11 which are analogous to Fig. 3.

ra/ - 20 -

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for treating raw unpeeled cold-stored potato tubers to inhibit greening due to chlorophyll develop-ment comprising applying an emulsion consisting essentially of a surfactant and water to said tubers in a quantity which is sufficient upon drying to form a thin continuous film of said surfactant thereon; said surfactant containing long chain fatty acid moieties, and at least one of polyoxyalkylene and polyhydroxy moieties and having an HLB rating of below about 15.

2. A method as claimed in claim 1 wherein said surfactant has an HLB rating in the range between about 8.5 and about 11.5.

3. A method as claimed in claim 1 wherein said emulsion contains up to about 15% of said surfactant.

4. A method as claimed in claim 3 wherein sufficient emulsion is applied so as to ensure a surfactant pick up on said coated tubers in the range 0.15 - 0.75 g/kg of tuber.

5. A method as claimed in claim 4 wherein said sur-factant is selected from the group consisting of: (a) long chain polyoxyethylene sorbitan fatty acid esters, (b) long chain sorbitan fatty acid esters and (c) long chain polyethylene glycol fatty acid esters.

6. A method as claimed in claim 4 wherein said sur-factant is Tween ? 85 (POE20-sorbitan trioleate) in an amount between 0.2 and 0.6 g/kg of tubers.

7. A method as claimed in claim 4 wherein said surfactant is Tween 81 - in an amount between 0.15 - 0.45 g/kg.

8. A method as claimed in claim 4 wherein said sur-factant is Span 20 - in an amount between 0.15 - 0.45 g/kg.

9. A method as claimed in claim 1 wherein said emulsion additionally contains an aliphatic hydroxy acid con-taining 3-6 carbon atoms or lactone thereof.

10. A method as claimed in claim 9 wherein said aliphatic hydroxy acid is selected from the group consisting of lactic acid, ascorbic acid, tartaric acid, isoascorbic acid and citric acid.

11. A method as claimed in claim 10 wherein said aliphatic hydroxy acid is present in an effective amount up to 15%.

12. Cold-stored potatoes coated with a continuous thin film of (a) a surfactant containing long chain fatty acid moieties, at least one of polyoxyalkylene and polyhydroxy moieties and having an HLB rating below about 15 or (b) a mixture of said surfactant with an aliphatic hydroxy acid containing 3-6 carbon atoms or lactone thereof.

13. Cold-stored potatoes coated with a continuous thin film of a surfactant containing long chain fatty acid moieties, at least one of polyoxyalkylen and polyhydroxy moieties and having an HLB rating below about 15.

14. Cold-stored potatoes coated with a continuous thin film comprising a surfactant containing long chain fatty acid moieties, at least one of polyoxyalkylene and polyhydroxy moieties and having an HLB rating below about 15 and an aliphatic hydroxy acid containing 3-6 carbon atoms or lactone thereof.

15. Potatoes as claimed in claim 12, 13 and 14 coated with 0.015 - 0.75 gms of surfactant per kg of potato.

16. Cold-stored potatoes as claimed in claim 14 wherein sail aliphatic hydroxy acid is selected from the group con-sisting of lactic acid, ascorbic acid, tartaric acid, iso-ascorbic acid and citric acid.