Stale Flavor Research Articles

Effect of Various Amino Acids on Elimination of Stale Flavor of Rice

After heating the aqueous model solution containing carbonyl compounds and amino acids, its reactivity was investigated by gas chromatography.1) At pH6.5, n-propionaldehyde easily reacted with L-arginine HCl, L-lysine HCl, L-histidine HCl, L-tryptophan and especially with L-cysteine. After heating, browning was found in each solution and volatile flavor of n-propionaldehyde was reduced. These amio acids reacted with n-capronaldehyde as well as n-propionaldehyde. The volatiles formed by the reaction between the carbonyls and L-cysteine were sulfurous flavor.2) On varying the contents of L-arginine HCl, L-lysine HCl and L-histidine HCl, about a half amount of carbonyl compound in the simple model system was made nonvolatile by addition of 5 fold amino acid in molarity to carbonyl compound. In case of the mixed model system of carbonyl compounds (1mM formaldehyde-1mM acetaldehyde-1mM n-propionaldehyde-1mM n-valeraldekyde-2.5mM n-carpronaldehype), L-lysine HCl or L-histidine HCl was most effective to make nonvolatile about a half amount of carbonyl compounds in model system. Its amino acid concentration was 20 fold in molarity to carbonyl compounds. L-cysteine made entirely nonvolatile carbonyl compounds in equal molarity to carbonyls.

Effect of Amino Acids on Elimination of Stale Flavor of Rice

Effect of Amino Acids on Elimination of Stale Flavor of Rice

Organoleptic Properties and Gas Chromatography Patterns of Steam Distillates from Fresh and Stale Milk Fat

We have examined the chromatographic patterns as well as the flavor characteristics of steam distillates of milk fat to obtain a more objective procedure than that given solely by taste panel evaluation for following the development of stale flavor during the storage of fat-containing dairy products. Both fresh and stale milk fats were steam deodorized at 50 and 75C at 1mm. Stale milk fat was also steam deodorized at 100 (1mm) and at 50C (3mm).One-millimeter pressure is preferable to higher pressures. Distillation at 75C or higher produces artifacts, volatile compounds generated from precursors, undesirable for following the formation of stale-flavor compounds during storage. Volatiles are recovered less completely at 50C than at higher temperatures, but artifact generation is low. Moreover, the flavor of volatiles recovered at 50C is characteristic of stale fat, and the chromatographie patterns of the 11 most prominent peaks correlate well with the flavor intensity and with the expected relative concentrations of the pertinent off-flavor compounds produced by storage of fats at various temperatures.

Chemical and Flavor Changes in Sterile Concentrated Milk During Storage

Three lots of concentrated milk (ultra-high temperature, high-temperature short-time, and conventionally sterilized) were stored at 4, 20, and 37C for eight months, and examined monthly for changes in flavor, volatile compounds as detected by GLC, acid degree values, and severity of browning. One lot of sterile concentrated skimmilk also stored at 4, 20, and 37C was analyzed occasionally during the eight months.Flavor deterioration was rapid at 20 and 37C, with cooked, scorched, and stale flavor defects most apparent. The ultra-high temperature milk had a flavor advantage initially, but after storage flavor scores for all processed milks were at similar levels. Some methyl ketones, furan, and methyl furan increased during storage at 20 and 37C. Milk fat was the precursor of 2-heptanone and 2-pentanone. Increases in acetone, butanone, acetaldehyde, furan, and methyl furan concentration during storage appeared to come from the nonfat portion of milk. Methyl sulfide was derived from the serum phase, but did not increase in concentration during storage. Methyl sulfide was the only volatile compound found at concentrations greater than its threshold value in milk. Acid degree values were high in all freshly sterilized milks and increased slightly at 20C and rapidly at 37C. Browning reaction values increased at 37C storage.

Gas Chromatographic Study of Flavor Deterioration in High-Temperature Short-Time Fluid Sterile Milk

Flavor changes which occur in high temperature short-time (HTST) fluid sterile milk during storage at 4.4, 22, and 36C for three months were investigated. The fluid milk was processed in a commercial steriliser at 140.5 C±1C for approximately 4sec.The physical changes observed in the HTST sterile milk during storage were: gelation, sedimentation, and creaming. Organoleptic evaluation revealed the development of stale flavor after two months at 22C. Rate of staling was a function of storage temperature.Flavor components isolated from the sterile milk were separated by gas-liquid chromatography (GLC) using a dual flame ionization detector. Flavor components tentatively identified in fresh samples were: ethanal, propanal, furfural, acetone, 2-butanone, ethanol, and butanol. Storage samples showed in addition to the aforementioned: butanal, hexanal, heptanal, 2-pentanone, and 2-heptanone.Confirmation of some carbonyl compounds tentatively identified by GLC was made by TLC of their 2,4 DNPH derivatives. Ethanal, acetone, and 2-butanone were identified in the controls, while ethanal, butanal, hexanal, acetone, 2-butanone, and 2-heptanone were identified in samples stored for three months at 22C.

Flavor of Recombined Milk

Anhydrous butteroil homogenized into reconstituted nonfat milk powder formed a recombined milk, the flavor score of which was relatively close to that of fresh pasteurized milk. When these milk components were packed in nitrogen and stored at -18C for six months no change in flavor of the recombined milk was noted. Higher storage temperatures caused changes in the butteroil which resulted in a stale flavor appearing in the recombined material. Recombined products made from butteroil stored at 27C for two months were judged definitely stale. Molecular distillation at 1 μ pressure at temperatures up to 200C removed from deteriorated butteroil some but not all of the components responsible for stale flavor. Under the packaging and storage conditions of the experiment, changes in the composition of the nonfat powder were not of sufficient magnitude to affect the flavor of the recombined milks.

Identification of Components in the Stale Flavor Fraction of Sterilized Concentrated Milk

SUMMARYThe more volatile components of the stale flavor fraction of sterilized concentrated milk (SCM) were studied by a nitrogen‐purge on‐column trapping technique. Higher‐boiling components were isolated by solvent extraction of the fat from lyophilized SCM, followed by low‐pressure reduced‐temperature steam distillation of the extracted fat. Components in the resulting flavor extract were identified by gas chromatography and mass spectrometry.The following compounds were identified in the extract from stale SCM: 2‐heptanone, 2‐nonanone, 2‐tridecanone, benzaldehyde, acetophenone, naphthalene, a dichlorobenzene, δ decalactone, benzothiazole and o‐aminoacetophenone. Of these compounds, only the dichlorobenzene and 2‐heptanone were identified in the extract from the control SCM.

Studies on Cereals Part IV

When stored rice (40°C, two months) was cooked, the stale flavor (komai-shu) was clearly detected by sensory test. Direct gas chromatographic analysis of head space vapors over cooked rice showed three main peaks which corresponded to propionaldehyde or acetone, n-valeraldehyde and n-caproaldehyde. On the other hand, the content of linoleic and linolenic acids of the rice decreased during storage at 40°C. This means that the unsaturated fatty acids autoxidized during storage and gave rise to carbonyl compounds responsible for the stale flavor of cooked rice.

Studies on Cereals Part V

When stored rice (40°C, two months) was cooked, the stale flavor (komai-shu) was clearly detected by sensory test. Direct gas chromatographic analysis of head space vapors over cooked rice showed three main peaks which corresponded to propionaldehyde or acetone, n-valeraldehyde and n-caproaldehyde. On the other hand, the content of linoleic and linolenic acids of the rice decreased during storage at 40°C. This means that the unsaturated fatty acids autoxidized during storage and gave rise to carbonyl compounds responsible for the stale flavor of cooked rice.

Direct Recovery of Off Flavors From Foam-Dried Whole Milk

Off-flavor compounds were obtained by a short-path migration at 1 μ pressure to a liquid nitrogen-cooled condenser, from dried milk warmed to 40C or less for 3 hr. Milks reconstituted from stale and oxidized powders, both before and after treatment, and market milk, both with and without the condensed volatiles, were evaluated by a five-man taste panel. The volatile flavors were oxidized, stale, unclean, astringent, and foreign. As with the author's earlier findings with regard to added ketones, the procedure is made more effective by first freeing the fat in the powder. Compounds recovered from a slightly stale dried milk gave a stale flavor to control milk, but their removal did not improve the residual powder. Compounds recovered from a strongly oxidized dried milk gave an oxidized flavor to control milk and their removal definitely improved the flavor of the residual powder. From four experiments with high free-fat oxidized dried milk, the average scores were: powder control—27.2; powder residue (powder control less volatiles)—30.7; milk control—37.8; milk plus volatiles—28.8.

Fractionation of the Stale-Flavor Components of Dried Whole Milk

Summary The stale flavor of dried whole milk has been shown to exist in two forms which can be separated by CCl 4 -vapor distillation and Girard's-T extraction. One is nonvolatile under the conditions employed but can be extracted from the milk fat with Girard's-T reagent; the other is volatile and is not recovered from the Girard's-T extract after hydrolysis of the resulting hydrazones. The Girard's-T extractible component is recovered more completely from the fat when lower concentrations of Girard's-T reagent are used, a behavior similar to aldehydes. It can be separated by paper or column chromatography into a stationary and a mobile component which contains the flavor. The R f value of the mobile component is similar to that of the reaction product of heptaldehyde. It is readily decomposed by alkali or 2,4-dinitrophenylhydrazine in 4 m HCl. On treatment with 2,4-dinitrophenylhydrazine, at least four carbonyl compounds were obtained as decomposition products and tentatively identified by paper chromatography as acetaldehyde, propionaldehyde, acetone, and either 2-butanone or 2-pentanone. The CCl 4 -vapor distillates were found to contain at least seven carbonyl compounds, five of which have been identified as formaldehyde, acetaldehyde, propionaldehyde, acetone, and 2-penatone. The remaining two compounds possess the spectra and chromatographic characteristics of a saturated monocarbonyl compound and either an unsaturated dicarbonyl or hydroxycarbonyl compound. The stale-flavor component of this fraction appears to behave like a dicarbonyl compound with Girard's-T reagent.

Effects of oxygen on quality and ascorbic acid retention in canned and frozen orange juices

AbstractA quantitative study has been made of changes in oxygen content, ascorbic acid content, flavour and colour during the processing and storage of pasteurised and frozen orange juices.By means of a gas‐saturation procedure, the juices were canned with initial oxygen contents ranging from about 3.5% to less than 0.002%.In frozen juices stored at o° F the presence of free oxygen in the cans for at least one year permitted slow oxidative loss of ascorbic acid.In pasteurised juices stored at 86° F, oxidative destruction of ascorbic acid occurred only during the first few days, since free oxygen rapidly disappeared from the cans. Throughout subsequent storage anaerobic loss of ascorbic acid continued at a rate about one‐tenth of that in the early period.Anaerobic reactions also contributed to flavour changes in pasteurised orange juices since complete removal of oxygen failed to retard the development of stale flavour at 86° F.

The Effect on Flavor of Using Substitute Fats in Dry Whole Milk

Summary Flavor deterioration in dry milks made with substitute fats was evaluated and compared with that of dry whole milk. Dried milks were prepared with cottonseed, peanut, soybean and coconut oils, and lard. All of these fats were at least partially hydrogenated with the exception of coconut oil, which was used in both hydrogenated and unhydrogenated forms. The findings of others (1, 3, 4, 9) that vacuum- or gas-packed dry whole milk develops a stale flavor, different from oxidized flavor, during early storage were confirmed. This off-flavor produced a substantial drop in the flavor score of both air- and vacuum-packed dry whole milks during the first month of storage. Such a flavor was not detected in any dry milks containing substitute fats. With the notable exception of coconut fat the substitute fats made dry milks with poor (oxidized) flavor qualities. Vacuum-packed dry milks made with coconut fat, either hydrogenated or unhydrogenated, exhibited good flavor after 6 months storage at room temperature.

Stale-Flavor Components in Dried Whole Milk. III. The Steam Distillation of Stale-Flavor Components from Stale Butter Oil

Summary The possibility of separating the stale-flavor component from stale butter oil by steam distillation was investigated. A procedure was developed by which a fraction was separated from the stale butter oil. This fraction, when dissolved in fresh butter oil and blended with fresh products to the composition of the original milk, yielded a detectable stale flavor in concentration as low as 6.2 parts per million. This procedure involves the steam distillation of stale butter oil under a pressure of 70mm. of mercury and at a temperature of approximately 45° C. The distillate is collected in water at 0° C. and the aqueous suspension is extracted with petroleum ether. The fraction containing the stale flavor then is obtained by evaporating the petroleum ether.

Stale-Flavor Components in Dried Whole Milk. II. The Extraction of Stale Butter Oil from Stale Dried Whole Milk by Organic Solvents

Summary In this study of the stale flavor which develops in dried whole milk on storage, it was necessary to develop a more efficient method for obtaining stale butter oil from the dried whole milk. An investigation of various Soxhlet-type extraction procedures with organic solvents resulted in two suitable procedures which yielded better than 90 per cent recovery of stale butter oil. Difficulties encountered in the removal of solvent from the extracted butter oil necessitated the development of a special technique to reduce the solvent concentration in the butter oil to the point where it did not interfere with the organoleptic judgment of the product. The stale-flavor component was extracted with the butter oil by these procedures in approximately the same ratio to the fat as existed in the original dried whole milk and therefore may be considered to be better than 90 per cent extracted from the dried whole milk.

Stale Flavor Components in Dried Whole Milk. I. The Distribution of Stale Flavor Between Fractions of Reconstituted Stale Whole Milk Powder

Summary Dried whole milk was prepared without homogenization and at low spray pressure in order to facilitate fractionation of the reconstituted milk. The powder was stored under varied conditions to insure a continuous supply of stale dried whole milk for this study. Reconstituted stale dried whole milk was separated mechanically into cream and skim milk at various temperatures of separation and rates of flow. The cream was churned into butter and buttermilk or washed with distilled water until it oiled off. The butter was melted, centrifuged and filtered, all at 40° C, to yield butter oil and butter plasma. The relative concentration of the stale-flavor component in the various fractions was determined by establishing the threshold concentration of the stale fraction when blended with an appropriate non-stale product to the approximate composition of the original whole milk. In all determinations made on the whole milk, cream, washed cream, butter and butter oil, the stale-flavor component appears to be distributed between these fractions according to their milk-fat content and therefore is concentrated in the milk-fat phase.