Effect of pasteurization, vitamin C supplementation and ultraviolet irradiation on the nitrosamine content of palm wine

Palm wine contaminated with varying quantities of the carcinogen dimethylnitrosamine (DMN) was subjected to heat treatments and ultraviolet irradiation. Dimethylnitrosamine (DMN) recoveries and nitrite concentrations were investigated by gas-liquid chromatography (g.l.c.) and colorimetry respectively. Whereas up to 2–6% of the initial DMN concentration was detectable in samples of the alcoholic beverage after raising the temperature of the fermenting drink to 62.5°C and also to 70°C and maintaining these for 30 and 10 min respectively, no nitrosamine was found in any of the palm wine samples treated for 20 min with UV light. Incorporation of 20 mg and 50 mg ascorbic acid into the pasteurized wine containing 2 μmol sodium nitrite, as well as increasing its acidity, appeared to enhance the disappearance of nitrite ions from the beverage.     

Kinetics of ascorbic acid degradation in potato blanching

Degradation kinetics of ascorbic acid was investigated on potato strips wrapped in aluminium foil and blanched for 5–60 min at different temperatures between 65°C and 100°C. The results confirmed that first order kinetics is adequate in describing the degradation reaction. The value of the rate constant was found to pass through a maximum at 85–90°C, indicating the inactivation of oxidative enzymes around these temperatures. Comparison of the degradation losses based on the present investigation with results on total loss of ascorbic acid during blanching reported in the literature showed that thermal degradation accounts for a considerable portion of the total loss.     

SPECIFICITY OF THE FERRIC-H2SO4 REAGENT FOR ALGINATES

SUMMARY— Alginate in foods was isolated from papain digests of the samples as the insoluble calcium salt. dispersed by sodium hexametaphosphate and a 1- to 5-ml aliquot of the dispersion 50–250 μg of sodium alginate) dried at 100°C. Heating of the anhydrous sample in the presence of the ferric-H₂SO₄ reagent for 12 min at 60°C produced a pink color with maximum absorption at 490–515 mμ and maximum density after aging for 90 min at 29±1°C. Under these conditions, proteins, amino acids (except tryptophane), other carbohydrates, vitamins. food additives and incipients did not interfere. The presence of water in the medium rendered the reaction nonspecific and increasing the temperature above 60°C or heating for longer periods at lower temperatures resulted in color formation by other polyuronides, especially pectin and pectic acid. Recoveries of alginate from several products were good: Milk, 94–98%; ice cream, 93.5–98%; pasteurized process cheese spread. 92.6-95%; chocolate milk, 92.4-95%; dietetic foods, 90-97.2%.     

The preparation of protein hydrolysate from defatted coconut and soybean meals

This study was conducted to determine the effects of temperature, time and concentration of acids on the hydrolysis of coconut and soybean meals. Using 6∼ hydrochloric acid (HCl), the complete hydrolysis of soybean meal was reached after 36 hr at 95°C, while it took only 24 hr to complete the process when 18 N sulphuric acid (H₂SO₂) was used at the same temperature. Coconut protein exhibited some degree of resistance to hydrolysis. Using 10 N HC1 and 18 N H₂SO₂ in two separate tests, it took 48 hr to complete hydrolysis at 95°C. Sulphuric acid caused a considerably greater decomposition of amino acids than HCl during longer periods of reaction with high acid concentration and temperature. Flavour development is a function of the free amino acids released which in turn is a function of acid concentration, reaction time and temperature.     

Reaction of nitrite with ascorbic acid and its significant role in nitrite-cured food

The decrease in concentration of free nitrite in an aqueous reaction solution made by mixing nitrite and ascorbic acid was studied. This decrease resulted information of a reaction product which transferred NO to ferricytochrome c to form ferrocytochrome c nitroso compound. From the solution containing the reaction product, nitrite could be regenerated spontaneously and suddenly by physical agitation. Oxygen was apparently not necessary for regeneration nitrite from the reaction solution. It does not seem that the regeneration of nitrite was responsible for a bimolecular dismutation of nitrosoascorbic acid in a reverse direction proposed by Fox and Thomson (Biochemistry2, 465; 1963). Heating of the reaction solution at less than 100°C resulted in a loss of nitrite from the solution, which was greater with increasing concentration of ascorbic acid. The reaction product formed between nitrite and ascorbic acid is probably responsible not only for nitrosation reactions, but also for the loss of nitrite observed during curing of meat.     

Quality of canned mushrooms acidified with glucono-δ-lactone

Summary The effect of sterilisation conditions (116 °C, 54 min; 121 °C, 24 min and 126 °C, 8 min) and acidification with glucono-δ-lactone as compared with other acids (citric, ascorbic and EDTA) on the yield and quality (colour, texture and taste) of canned whole mushrooms, has been studied using previously refrigerated raw material (1.5 or 2.5 days at 2 °C). Colour measurement of canned mushrooms by the determination of the L* parameter of ten mushroom pilei probed to be the most suitable method, among those studied, shown the greater F parameter in a variance analysis. Yield was higher when the raw material was stored under refrigeration for longer. Yield, texture and colour improved with the Highest Temperature and Shortest Time process (126 °C, 8 min). Glucono-δ-lactone appears to be a more suitable acidulant than citric acid as it provides equal colour, texture and yield without conferring as acid a taste as citric or an extraneous flavour.     

Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.     

Repeated Regeneration of Degraded Red Beet Juice Pigments in the Presence of Antioxidants

Ascorbic, isoascorbic, metaphosphoric, and gluconic acids improved the regeneration of red beet juice pigments after heating, and resulted in greater retention of the pigments during processing and storage. Their effect varied depending on the pH of the juice solutions. Ascorbic and isoascorbic acids allowed for the greatest regeneration at pH 3.8. At pH 6.2, metaphosphoric acid and gluconic acid were more effective. Addition of ascorbic acid once prior to the first heating retained the initial concentration of pigments even after 5 cycles of heating (3 min at 100°C) and regeneration. Control solution lost red pigments completely.     

EFFICACIES OF ACETIC, LACTIC AND TWO MIXED ACIDS IN REDUCING NUMBER OF BACTERIA ON SURFACE OF LEARN MEAT

This study on sanitizing beef surfaces was designed to evaluate effects of mixtures of acetic, lactic, citric and ascorbic acids with individual solutions of acetic and lactic acids. Acetic acid (3%), lactic acid (3%), MA1 (2% acetic, 1% lactic, 0.25% citric and 0.1% L-ascorbic acids) and MA2 (2% lactic, 1% acetic, 0.25% citric and 0.1% L-ascorbic acids) solutions were applied to beef core samples of muscle inoculated with bacteria. Experimental variables were type, concentration and temperature of acid solutions and type of microorganisms. Overall, an increase in either acid concentration or treatment temperature decreased numbers of residual viable bacteria. Lactic acid solution was the most effective against S. typhimurium with a reduction of 2 log₁₀ at 70°C. For enterobacteria, acetic, lactic and MA2 solutions at 70°C resulted in a 1.5 log₁₀ reduction. MA2 was the most effective acid solution at both 45 and 70°C, whereas, lactic acid and the MA2 mixture did not differ in effectiveness at 20°C.     

Quality attributes of frozen okra as influenced by processing and storage

Sensory evaluation and chemical analyses were carried out on unblanched, steam-blanched (5 min, 100°C) and water-blanched (3 min, 98°C) okra held in frozen storage (–18°C) for 4, 8, 12 and 32 weeks. Hot water-blanched frozen okra compared favourably with fresh samples, even after 32 weeks, in colour, flavour and overall acceptability and was superior to steam-blanched and unblanched except in viscosity. Blanching, especially in steam, improved ascorbic acid retention during frozen storage. Little change in protein occurred.     

Reduction of chilling injury in ripe Alphonso mango fruit in cold storage by temperature conditioning

The influence of ripening temperature and cold conditioning of pre-climacteric fruits on the incidence of chilling injury (CI) in ripe mango fruits cv. Alphonso during refrigerated storage was investigated. Fruits previously held and ripened at tropical ambient temperature (AT, 27–34°C) developed CI (skin staining or browning) when ripe fruits were subsequently stored at 5, 10, or 15°C for shelf-life extension. Fruits held and ripened at 20°C1°C, RH 85–90% showed little evidence of CI when subsequently stored at 5 or 10°C up to 14 days. Chilling injury in ripe mangoes was also avoided by holding pre-climacteric fruits for a minimum period of 30 days at 10°C and then ripening them at 27–34°C. The quality of the ripe mangoes remained good during cold storage for 7 days and were acceptable until 10–14 days with minimal changes in texture, flesh colour, carotenoids, total soluble solids, titratable acids and ascorbic acid. Shelf-life of ripe mangoes can thus be extended under refrigeration by pre-storage conditioning.     

Determination of a process time for a new product: canned low acid artichoke hearts

In order to obtain a process time for canned low acid artichoke hearts, the heat resistance of Clostridium sporogenes PA 3679 in phosphate buffer (pH 7) and in artichoke puree (pH 5.2) was determined in the range of 100–118°C. D _T values in artichoke puree were determined by the most probable number and plate count methods. D _121°C values were deduced by extrapolation of the curves. An F 8.3/121 (see nomenclature section) target value of 1.8 min, equivalent to an F ₀= 2.5 min, was established considering a D _121°C value of 0.36 min for artichoke puree. The cold point for canned artichoke hearts in 1/2 kg (71.5x117 mm) cans was determined, a set of heat penetration and cooling curves were obtained and the values of the parameters ' j ' and ' f ' were found. A process time was deduced, 21.5 and 23 min of heating at 121°C, following the methods of Patashnik (1954) and Hayakawa (1970, 1974) respectively, in order to reach the F ₀ target of 2.5 min for this new canned food. This process was adequate, as the inoculated experimental pack test showed no altered cans out of 50 inoculated after 21.5 min of heating at 121°C.     

Enhanced deactivation of bacterial lipases by a modified UHT treatment

Lipase was produced by three non-fluorescent pseudomonads during culturing in resterilized UHT whole milk at 10°C. The enzymes exhibited pronounced thermostability in milk with 85–88 and 82–89% of the original activities retained after heat treatments at 140°C for 5 sec and 80°C for 10 min, respectively. Also, after a single treatment at 60°C for 10 min approximately 95% of the untreated activities remained.
Double heat treatments consisting of either 130 or 140°C for 5 sec followed by 60–80°C for 3 min enhanced lipase deactivation by as much as 40% compared with the combined effect of both higher and lower temperature treatments performed on separate enzyme samples. No significant enhancement of deactivation was noted when samples were heated at 60°C for 3 min followed by 140°C for 5 sec compared with the latter treatment alone.
Lipase deactivation was non-linear at 60°C following treatment at 140°C for 5 sec; no substantial additional loss of activity occurred at the lower temperature between 5 and 10 min.     

Effect of polyphenol and pH on cocoa Maillard-related flavour precursors in a lipidic model system

Polyphenol and pH influence the flavour quality of cocoa beans during roasting. Amino acids and reducing sugars are flavour precursors in cocoa beans, which develop into cocoa-specific aroma through Maillard reactions during roasting. A central composite design was applied to determine the combined effect of polyphenol and pH on the flavour precursors during cocoa roasting at 120 °C for 45 min using a lipidic model system. Polyphenol was added at 40, 80 and 120 g kg⁻¹ and pH was adjusted to 4.5, 6 and 7.5. The response surface methodology revealed that a lower concentration of amino acids and reducing sugars was obtained at higher polyphenol concentration (120 g kg⁻¹) and lower pH value (4.5). Based on the constraints set, the best polyphenol concentration of 43–58 g kg⁻¹ and pH of 7.0–7.5 was found to be optimum for the formation of flavour precursors in this lipidic model study.     

STABILIZATION OF ANTHOCYANINS IN FROZEN TART CHERRIES BY BLANCHING

SUMMARY— Unpitted red tart cherries (Prunus cerasus L. cv. Montmorency) were blanched in steam (100°C) for 0, 30, 45 and 60 sec, then frozen at −20°C. The anthocyanin color of the fruit was determined periodically during frozen storage for 3 months in one experiment and 10 months in another. When the cherries were not allowed to thaw before the analysis, no color loss due to anthocyanin destruction was observed in either the blanched or unblanched cherries. When they were thawed at room temperature (22° C) in single layer for 2 and 4 hr, the unblanched cherries lost 14 and 25% anthocyanin color, respectively; cherries subjected to 45- or 60-sec blanching showed no significant color loss. When the cherries were disintegrated in a Waring Blendor for up to 30 min, the unblanched cherries lost considerable color (70%) after 30 min under oxygen or air, but those blanched for 45 or 60 sec suffered no color loss. Some anthocyanin destruction was Observed in the 30-sec blanch lot. Blending under oxygen was slightly more deleterious to the color than blending under air. Blending under nitrogen minimized the color loss but did not eliminate it. Blanching resulted in a 4–7.5% loss of weight.     

Stabilized soymilk for ambient tropical storage: a preliminary report

The shelf-stability of soymilks prepared from sterilized (121°C for 15min) water-soluble extracts of sprouted-blanched, sprouted-unblanched, and blanched whole soybeans (control) was evaluated; samples were compared for coagulation, pH, and loss of starch. The extract from sprouted-blanched soybeans remained uncoagulated for 6 weeks in ambient tropical storage, showed the greatest loss of starch and had the least total solids content (10%). The sprouted-unblanched soybeans produced an extract which coagulated instantly after sterilization at a pH of 5.6, the lowest pH value for treatment and control samples. The control contained the highest total solids (25%), showed least loss of starch and coagulated after 2 days in ambient tropical storage.     

假植后低温处理对水芹贮藏效果的影响

研究水芹在常温、低温和假植后低温鲜切条件下的呼吸强度、水分、叶绿素、抗坏血酸、还原糖和氨基酸含量等指标在贮藏过程中的变化。结果表明：假植后低温鲜切处理的水芹失水少,叶绿素、还原糖、抗坏血酸和游离氨基酸保存率高,耐藏性好,其呼吸强度高于低温鲜切的水芹,同时假植后低温鲜切处理能够显著延缓褐变的速度,而常温贮藏的保鲜效果最差;鲜切水芹在3～5 ℃条件下贮藏18 d,感官质量基本不变。     

Activity of ε–Polylysine Against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes

ABSTRACT: ε–polylysine is a homopolymer of L-lysine, an essential amino acid, with a reportedly wide antimicrobial spectrum. This study evaluated the antimicrobial activity of ε–polylysine, as compared with known preservatives and organic acids, against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes , in culture broth. The compounds tested included ε–polylysine (0.0025% to 0.05%), sodium diacetate (0.25%), sodium lactate (3.0%), lactic acid (0.1%), and acetic acid (0.1%), alone, as well as in combination with ε– polylysine (0.0025% to 0.03%); all treatments were evaluated in tryptic soy broth supplemented with 0.6% yeast extract. Treatments were inoculated (approximately 2 log colony-forming units [CFU]/mL) with 5-strain ( E. coli O157:H7, S. Typhimurium) or 10-strain ( L. monocytogenes ) mixtures of the pathogens. Survival/growth of the inoculated bacteria was periodically monitored during incubation at 4 °C (30 d) and 24 °C (48 h). Bactericidal effects of ε–polylysine were obtained against E. coli O157:H7 and S. Typhimurium at 4 °C. At the same temperature (4 °C), ε–polylysine alone or in combination with other compounds tested inhibited growth or was bactericidal against L. monocytogenes. All 3 pathogens were inhibited by ε–polylysine at 24 °C; however, L. monocytogenes was the most sensitive and S. Typhimurium the most resistant. The antimicrobial activity of ε–polylysine against E. coli O157:H7 and S. Typhimurium was enhanced ( P < 0.05) when tested in combination with sodium diacetate or acetic acid. Combination treatments with sodium lactate resulted in loss of ε–polylysine activity by the end of the incubation period. Overall, under the conditions of this study, ε–polylysine exhibited antimicrobial effects against the 3 pathogens tested.     

Effect of delayed icing on the storage life of rainbow trout

Rainbow trout ( Salmo irideus ), were divided into groups: (1) iced immediately, or (2) kept at 10 °C for 6 hr, (3) 20 °C for 6 hr, (4) 20 °C for 18 hr, (5) 30 °C for 4 hr, (6) 30 °C for 6 hr. Fish in groups 2–6 were iced at the end of the stipulated temperature/time period of holding. Quality was subsequently assessed every 2 days for 14 days during iced storage: sensory assessment using criteria of appearance, texture and odour; chemical assessments by measurement of total volatile bases, hypoxanthine and thiobarbituric acid: microbiological assessments by total bacterial counts at 20 °C/72 hr and 37 °C/48 hr incubation. The results indicate that deamination due to bacterial action and hydrolysis of fats increases progressively with rising temperature prolonged periods of storage prior to icing, and results in final spoilage. Fish iced immediately after delivery and those iced after being kept at 10 °C for 6 hr were acceptable to quality even after 14 days of iced storage. Recommendations are made for maintenance of quality and extension of shelf life.     

Some effects of modified-atmosphere packaging and vacuum packaging in combination with antioxidants on quality and storage life of chilled potato strips

A modified-atmosphere packaging system for chilled fresh potato strips, which rapidly produced oxygen levels < 3%, was identified. This system enclosed the strips within 25 μ low density polyethylene film heat sealed to a fibre tray lined with Surlyn-PVdC-Surlyn, and the package flushed with an initial atmosphere of 5% O₂, 10% CO₂. An equilibrium-modified atmosphere of 3–4% CO₂, 1–2% O₂ was established after 3 days' storage at 5°C. This modified-atmosphere package, used in combination with dipping of potato strips in a 10% ascorbic acid solution, inhibited enzymatic discoloration for 1 week at 5°C. Vacuum packaging within a Surlyn/PVdC-coated polyester film, with or without dipping in ascorbic acid solution, inhibited discoloration of chilled potato strips stored at 5°C for at least 2 weeks.