Lipid stability in powdered infant formula stored at ambient temperatures

Lipid stability of standard infant formula was evaluated at ambient temperatures, namely 25, 30 and 37 °C, during 3 months. Lipids were thoroughly analysed to evaluate changes in fatty acid composition and trans fatty acid isomers, non‐volatile oxidation compounds including oxidised, dimeric and polymeric triacylglycerols, and tocopherol. No significant changes in either of the parameters examined were found in total lipids extracted from infant formula along the storage period. However, the minor free oil fractions (about 7.5% of total lipids) showed a significant increase in oxidation compounds and marked decrease in tocopherol levels during storage at all temperatures. Samples stored at 37 °C for 3 months were rancid and, accordingly, contained the highest oxidation level in the free oil fraction, whereas total lipids extracted were apparently not oxidised. Results showed the necessity of analysing separately the free oil fraction in infant formulae to obtain a clear picture of the oxidation status.     

Quality maintenance of minimally processed Chinese cabbage with low temperature and citric acid dip

Chinese cabbage (Brassica campestris L pekinensis group) was minimally processed using best preparation techniques and stored at 0 and at 5°C with and without dips in either citric acid, calcium chloride or ascorbic acid, all at 10 g litre⁻¹. The visual quality, degree of chilling injury, pH and taste were evaluated. The most deleterious effects on quality were produced by black speck (gomasho) and browning. Citric acid inhibited the development of black speck and extended storage life from 10 days of the control to 14 days at 5°C. At 0°C the storage life was not extended by any dip, but citric acid improved quality by reducing black speck. Minimally processed Chinese cabbage treated with citric acid showed only a slight reduction of pH from 6·3 of the control to 6·1 (P⩽0·05) and taste was not significantly affected (P>0·05). Microbial spoilage was not apparent during storage at 0°C for 35 days and 5°C for 21 days under any treatment. © 1997 SCI.     

Pressurized acidified water extraction of black carrot [<Emphasis Type="Italic">Daucus carota</Emphasis> ssp. <Emphasis Type="Italic">sativus</Emphasis> var. <Emphasis Type="Italic">atrorubens</Emphasis> Alef.] anthocyanins

The anthocyanins present in black carrot were extracted with pressurized water acidified with sulfuric, citric and lactic acids. Anthocyanin degradation became significant above 100 °C and there was no improvement when extraction pressure was increased to 100 bar. Therefore, the extraction from black carrot was carried out at temperatures 50, 75 and 100 °C under 50 bar pressure. The extraction efficiencies in terms of acylated and non-acylated anthocyanins were comparable for all three acids used to acidify water at 50 °C, while similar results were observed at 75 °C for both citric and lactic acids. Water acidified with lactic acid showed significantly higher extraction efficiency at 100 °C compared to water acidified with sulfuric and citric acids. Highest degree of polymerization together with increasing degree of browning was observed within extracts when sulfuric acid was used. On the other hand, when organic acids were used to acidify water, a higher extraction efficiency of anthocyanins, accompanied with a relatively low polymerization and browning was observed, with lactic acid giving the best results.     

Effects of seed roasting temperature and time on the quality characteristics of sesame (Sesamum indicum) oil

The quality characteristics and composition of sesame oils prepared at different roasting temperatures (160–250°C) from sesame seeds using a domestic electric oven were evaluated as compared to an unroasted oil sample: only minor increases (P<0·05) in characteristics, such as peroxide value, carbonyl value, anisidine value and thiobarbituric acid reactive substances, of sesame oils occurred in relation to increasing roasting temperature and time between 160 and 200°C, but colour units of oils increased markedly over a 220°C roasting temperature. Significant decreases (P<0·05) were observed in the amounts of triacylglycerols and phospholipids in the oils prepared using a 250°C roasting temperature. The amounts of γ-tocopherol and sesamin still remained over 80 and 90%, respectively, of the original levels after roasting at 250°C. In the oil prepared using a 250°C roasting temperature, sesamol was detected at 3370 mg per kg oil, but sesamolin was almost depleted after 25 min of roasting. Burning and bitter tastes were found in the oils prepared at roasting temperatures over 220°C. The results suggested that a high-quality product would be obtained by roasting for 25 min at 160 or 180°C, 15 min at 200°C and 5 min at 220°C when compared with the other samples. © 1997 SCI.     

Some factors affecting the rate of protease catalysed reactions

The rates of hydrolysis of casein catalysed by bacterial proteases were determined at different pH values and temperatures. The bacterial proteases Maxatase and Alcalase were active in the pH range 6·7–9·0 with a maximum rate at pH 6·7 when the temperature was 37°C. However, even at pH 9·0, activity is still quite satisfactory. The reaction rates of the two enzymes at 45°C were higher than those at 37°C when the pH value was 8·2. The rate of the Maxatase catalysed reaction was more than that of Alcalase at 45°C. The activation energies were calculated and, as expected, it was found that the higher the enzyme reaction rates, the lower were the activation energies.     

Effect of Chitin as Coagulating Aid on Protein Yield, Composition and Functionality of Tomato Seed Protein Concentrates

The effectiveness of chitin as coagulating aid, protein coagulants and coagulation temperatures in recovering tomato seed proteins, and their effect on composition and emulsion properties of tomato seed protein concentrates (TSPC) were investigated. Citric acid, hydrochloric acid, or a mixture of citric acid and hydrochloric acid were used and chitin addition ranged from 0 to 1.0% (protein basis). Coagulation temperatures employed were 25°C, 60°C or 95°C. Samples with no chitin added resulted in significantly (P < 0.05) lower protein yields than samples with chitin addition. Ash content of the TSPC was significantly (P < 0.05) affected by chitin addition and coagulation temperature. Lowest crude fat content was obtained with citric acid at 25°C. Lowry protein and total nitrogen was highest without chitin addition. Samples coagulated at 25°C showed highest emulsion ability and emulsion stability. The least stable emulsions were produced with hydrochloric acid. Chitin addition did not affect emulsion properties.     

Antioxidant Properties of Caffeic acid Phenethyl Ester and 4‐Vinylcatechol in Stripped Soybean Oil

Caffeic acid was used to synthesize 4‐vinylcatechol (4‐VC) by thermal decarboxylation and to prepare caffeic acid phenethyl ester (CAPE) by esterification reaction. The identities of synthesized products were confirmed by ¹H NMR. Antioxidative activities of 4‐VC and CAPE were compared with α‐tocopherol and BHT in stripped soybean oil at 60 °C under the dark. To evaluate the degrees of oxidation at different concentrations and combinations, peroxide value (PV) and ¹H NMR were performed. From the results of PV, the formation of primary oxidation products (i.e., hydroperoxides) in stripped soybean oil containing 200 ppm CAPE was the slowest. The relative oxidation degree of 200 ppm CAPE (9.5%) was lower than other samples on 9 d. Similar results were obtained by ¹H NMR analysis. After 15 d of storage, levels of conjugated diene forms and aldehydes of 200 ppm CAPE sample (57.3 and 0.9 mmol/mol oil) were also lower than other treatments. In addition, 4‐VC and α‐tocopherol were found to have a synergistic antioxidant effect.     

Effect of Crystalline Structure on Oxidation of Fish Oil in Stearin:Fish Oil Mixtures

Effects of incorporation of stearin fraction into fish oil on crystallisation behaviour and oxidative stability of fish oil were examined. The stearin fraction (S₂₅) was obtained from step-wise dry fractionation of anhydrous milk fat at 25 °C. Analysis of fatty acid composition by gas chromatography showed that unsaturated fatty acids (89.3 %) were enriched in the fish oil whereas the S₂₅ typically comprises of saturated fatty acids (79.4 %). A series of S₂₅:fish oil mixtures (0:100, 25:75, 50:50, 75:25; 90:10 and 100:0) was prepared by mixing the S₂₅ and fish oil at 50 °C under flushing of nitrogen gas. Crystallisation and thermal properties and crystal structures of the mixtures were investigated by differential scanning calorimetry and small- and wide-angle X-ray scattering, respectively. The crystallisation/melting temperatures and crystallisation/melting enthalpies of the mixtures increased with increasing ratios of S₂₅ blended into fish oil. All mixtures showed similar crystal structures (double- and triple-chain length) and crystal polymorphs (α, β’ and β) at 4 °C. A decrease in S₂₅ fraction in the mixtures caused a higher proportion of triple-chain length crystal packing and β polymorph. Measurement of peroxide values of the mixtures upon storage at 8 °C for 42 days showed that blending as low as 25 % S₂₅ sufficiently delayed the lipid oxidation of fish oil by about two-fold and the rancidity threshold to 16 days instead of 9 days for fish oil only. This study demonstrates that mobility of oxygen and triacylglycerol (TAG) molecules in fish oil can be restricted by crystalline state of milk fat, in turn, limiting the propagation of oxidative reaction in fish oil.     

Temperature Dependence of Autoxidation of Perilla Oil and Tocopherol Degradation

Abstract: Temperature dependence of the autoxidation of perilla oil and tocopherol degradation was studied with corn oil as a reference. The oils were oxidized in the dark at 20, 40, 60, and 80 °C. Oil oxidation was determined by peroxide and conjugated dienoic acid values. Tocopherols in the oils were quantified by HPLC. The oxidation of both oils increased with oxidation time and temperature. Induction periods for oil autoxidation decreased with temperature, and were longer in corn oil than in perilla oil, indicating higher sensitivity of perilla oil to oxidation. However, time lag for tocopherol degradation was longer in perilla oil, indicating higher stability of tocopherols in perilla oil than in corn oil. Activation energies for oil autoxidation and tocopherol degradation were higher in perilla oil (23.9 to 24.2, 9.8 kcal/mol, respectively) than in corn oil (12.5 to 15.8, 8.8 kcal/mol, respectively) indicating higher temperature-dependence in perilla oil. Higher stability of tocopherols in perilla oil was highly related with polyphenols. The study suggests that more careful temperature control is required to decrease the autoxidation of perilla oil than that of corn oil, and polyphenols contributed to the oxidative stability of perilla oil by protecting tocopherols from degradation, especially at the early stage of oil autoxidation.     

A chemiluminescence study of the oxidation of vegetable oils and model compounds and the effects of antioxidants

Chemiluminescence was used to study the course of oxidation of sunflower oil samples at a number of temperatures between 70 and 121°C. The induction time was determined for each sample and used to estimate the shelf life of the oils at 25°C. In addition, Chemiluminescence during oxidation in air on alumina at 80°C was used to study both sunflower oil and, as a model compound, methyl linoleate with and without added artificial antioxidants. By using the method of inhibitors, the reaction rate and level of hydroperoxide were determined. It was also possible to determine the level of naturally occurring antioxidant in the vegetable oil.     

Inhibition of oxidative rancidity in frozen cooked fish flakes by tert-butylhydroquinone and rosemary extract

The antioxidant properties of tert-butylhydroquinone (0·5 g kg^?1 + 20 g kg^?1 ascorbic acid—TBHQ-AS) and an extract of rosemary (2·5 g kg^?1) alone and in combination were determined by their addition as solutions to cooked fish flakes stored at - 20°C. Oxidation was measured by following changes in free fatty acids, thiobarbituric acid number, fatty acid composition and sensory evaluation. The order of effectiveness in inhibiting oxidation was TBHQ-AS > combination > rosemary > untreated control ?70°C > untreated control -20°C. Sensory evaluation indicated that green aroma and flavor notes were associated with the rosemary extract, while fish oil notes were associated with untreated samples.     

The influence of temperature on shortening and rigor onset in beef muscle

At sufficient ATP concentration and temperatures below about 15°C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 6·3–6·0 and at about 2 μMol ATP/g muscle, cold shortening can begin at pH around 7·0 and the full ATP concentration (4 μMol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (?1°C) and physiological temperatures (38°C) starts at various pH values and ATP concentrations in the muscle. At 38°C the rigor onset occurs at pH 6·25 and about 2 μMol ATP/g muscle, dropping at 15°C to pH 5·75 and 1 μMol ATP/g muscle. At 0°C, as at all temperatures below 10°C, the loss of extensibility at medium loads (about 250 g/cm²) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0°C with pH of 6·1–6·2 and 1·8–2·0 μMol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rôle.Maximum loss of extensibility or completion of rigor is reached between 10°C and 38°C at pH 5·5–5·6 and less than 0·5 μMol ATP/g muscle. At 0°C the completion of rigor takes place at pH 6·0, but still at 0·5 μMol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures.The results are discussed in terms of changes in the concentration of Ca²⁺ ions and ATP.The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.     

Microwave pasteurisation of prepared meals

Pasteurising ready-to-eat meals in their retail packaging extends their shelf life. Temperatures above 80°C are required to pasteurise a wide variety of products. The ability of microwave systems to produce these temperatures in packs of spaghetti bolognaise, without reducing product quality, was investigated using a domestic microwave oven (2450 MHz; multi-mode; 0·2, 0·36 or 0·6 kW; 240 or 300 s residence time), a pilot-scale tunnel (2450 MHz; multi-mode; 6 kW, 125 or 158 s residence time) and a further pilot-scale tunnel (896 MHz; single-mode; 7 kW, 144 s residence time).Product temperature distribution after microwave heating was measured using nine thin wooden rods with two thermocouples attached to each. The probes were inserted near the four corners of the product, at the centre and mid-way along each edge.Mean product temperatures above 80°C could be achieved using any of the systems but only the tunnel operating at 896 MHz heated all of the product in a pack above that temperature. The multi-mode systems produced the least uniform heating, the coldest regions being located at the centre and the hottest at the corners of products. Temperature differences measured within individual products after heating in the domestic oven and the 2450 MHz tunnel were up to 66°C and 36°C, respectively. In the 896 MHz tunnel temperatures at the corners were lower than at the edges and mean temperatures of 90°C were achieved with standard deviations (six replicates) of < 6°C and a maximum temperature difference of 17°C within a single product.     

Fatty acid composition and oxidation of cowpea (Vigna unguiculata) flour lipid

The lipids extracted from cowpea flour before and after storage at water activities (a_w) of 0·11, 0·33 and 0·75 and at 5, 25 and 40°C for 6 months were examined for their fatty acid composition and oxidation.Linoleic, linolenic and oleic acids, in decreasing order, were the unsaturated fatty acids recorded. The saturated fatty acids were palmitic, stearic and arachidic in decreasing order. The total unsaturated fatty acids concentration was higher than the total saturated fatty acids, with palmitic acid being the single dominant fatty acid.$\text{Saturated}\text{unsaturated}$ fatty acid ratios ($\text{s}\text{u}$ ratio) and lipid conjugated diene absorbance at 233 nm indicated that the a_w of 0.33 and the storage temperature of 5°C were the most effective in mitigating the oxidation of the cowpea lipid.Oxidation rates of the unsaturated fatty acids were related to their levels of unsaturation.     

Effect of temperature and pH on the formation of higher alcohols,fatty acids and esters in the malt whisky fermentation

The levels of higher alcohols, fatty acids and esters in small-scale whisky fermentations which were carried out at different temperatures and initial pH values were investigated. Neither the total higher alcohol content nor the relative abundance of different alcohols was affected by varying the temperature between 20 and 30°C. However, the level of octanoic acid, decanoic acid, ethyl hexanoate and ethyl octanoate were depressed at higher temperatures. The highest level of acetate esters were observed at 25 and 30°C. Altering the initial pH of the wort had little effect on the level of higher alcohols. However, increasing the pH from 4·0 to 7·0 resulted in an increase in the level of octanoic, decanoic and dodecanoic acids. Maximum levels of acetate esters of higher alcohols were obtained when initial pH values of between 5·0 and 6·0 were used.     

Effect of black tea, garlic and onion on corn oil stability and fatty acid composition under accelerated oxidation

Fresh black tea, garlic bulbs and onion skin were macerated in refined corn oil to evaluate their antioxidant properties and the effect of heat on oil stability and fatty acid composition in accelerated oxidation experiments at 55 ° and 140 °C. At the lowest temperature control and onion treatments showed an induction time of 3 days with maximum peroxide values of 62 and 45 meq kg^?1, respectively. Addition of black tea and garlic increased oil stability with peroxide values of 5 meq kg^?1, without appreciable changes in the fatty acid composition. Heating at 140 °C for 48 h produced an accelerated deterioration of corn oil in all treatments. A reduction of polyunsaturated fatty acids of about 40% was observed, with high concentrations of non‐eluted materials which contained thermo‐oxidized substances. It was found that natural extract of black tea and garlic were effective to preserve corn oil under accelerated oxidation at 55 °C which simulates oil behaviour during storage, but cannot reduce the rate of oxidation at frying temperatures.     

Prevention of enzymatic browning of apple cylinders using different solutions

Inhibition of enzymatic browning and decay on cut surfaces of Golden Delicious apple using ascorbic acid, cysteine, sodium chloride, calcium chloride, citric acid and sodium ascorbate alone or in combinations was investigated at 4 and 10 °C for a storage period of 0, 7 and 14 days, in an attempt to find the most effective treatment. Apple segments immersed in ascorbic acid and citric acid alone showed visual traces of browning after 7 days storage at 4 °C. After 14 days storage, only ascorbic acid and ascorbic acid plus sodium chloride had moderate browning, while all other treatments were severely affected. However, at 10 °C, only ascorbic acid was effective in reducing the level of browning, although its effect was minimal after 14 days storage. Browning was more severe at 10 °C than 4 °C in all solutions. The browning measurement (a* value) became increasingly positive from 7‐ to 14‐day storage. Microbial decay was absent in all treatments within 7 days at 4 and 10 °C. However, three test solutions showed microbial decay after 14 days storage at 10 °C in addition to the control solution, which showed decay at both 4 and 10 °C storage temperatures.     

Stability of α-L-aspartyl-L-phenylalanine methyl ester hydrochloride in aqueous solutions

The stability of USAL (α-L-aspartyl-L-phenylalanine methyl ester hydrochloride) was studied in solutions in relation to the pH value (1.10–6.95 at 20 °C), the temperature (20–80 °C at pH 2.2) and the ionic strength (0.16–2.0 at 20 °C and pH 4.0). The effects of pH and temperature of the medium were very significant. From the point of view of the stability the optimum pH value lies in the pH range 2.5–4.5 and at lower temperature. The ionic strength did not affect the stability in the tested range. The effects of citric acid (0–10%) and sucrose (0–75%) were also investigated. An addition of citric acid exhibited an effect on USAL stability corresponding to the shift of pH value that it caused. The occurrence of sucrose in the solution had a favorable effect at higher concentrations.     

Tomato Seed Protein Concentrates: Effects of Methods of Recovery Upon Yield and Compositional Characteristics

Tomato seed protein concentrates (TSPC) were recovered from ground tomato seeds using alkaline extraction and three different protein coagulants (citric acid, citric acid/hydrochloric acid mixture or hydrochloric acid) at three coagulation temperatures (25°C 60°C or 95°C). The effect of this 3 × 3 protein recovery matrix on protein yield and composition of the freeze-dried TSPC was studied. No significant effect of protein coagulants on protein yield (TCA/heat coaguable protein) was found but it was significantly higher with samples coagulated at 25°C than when heat coagulation was applied. Coagulation procedures at room temperature resulted in lower moisture, crude fat and ash concentration than heat coagulated samples. Lowry protein content of TSPC was not significantly affected by recovery methods but crude protein content after coagulation with citric acid resulted in significantly higher values of the samples coagulated at 25°C than those at 95°C.     

Efficacy of media for promoting ascospore formation by Neosartorya fischeri,and the influence of age and culture temperature on heat resistance of ascospores

Gorodkowa agar (GA), Fowell's acetate agar (FAA), Kleyn's acetate agar (KAA), McClary's acetate agar (MAA), grape juice agar (GJA), apple juice agar (AJA) and vegetable juice agar (VJA) were evaluated for their efficacy to promote ascospore formation by three strains of Neosartorya fischeri. All three strains produced abundant mature ascospores when grown on FAA, GJA and AJA, but not on the other test media. Ascospores produced on GJA developed greater heat resistance with time when suspended in commercial apple juice (AJ), grape juice (GJ) and 0·1 M potassium phosphate buffer (PB) during heat treatment. From 10 to 13 days of incubation at 30°C, decimal reduction times at 80°C (D_80°C values) for ascospores increased from 27·0 to 66·7 min in AJ, 28·5 to 33·3 min in GJ and 18·2 to 50·0 min in PB. The rate of development of heat resistance was dependent upon the incubation temperature at which ascospores were produced. After treatment at 70°C for 60 min, survival percentages for 21-day-old ascospores were 0·32, 8·13, 54·95 and 53·70% of ascospores produced at 18, 21, 25 and 30°C, respectively. At 42 days, 0·23 and 38·02% of ascospores produced at 18 and 21°C, respectively survived 85°C for 30 min; this treatment did not inactivate 42-day-old ascospores produced at 25 and 30°C. During a 114-day test period, ascospores produced at all incubation temperatures became dormant to some extent and required heat activation to facilitate germination.