Acceleration of ageing in rice stick noodle sheets using low temperature

The objectives of this research were to study the effects of temperature and time on ageing of rice stick noodle sheet retrogradation, and to estimate the effect of accelerated ageing on the eating qualities of the noodles. Hardness was used as a textural index due to a good correlation between instrumental and sensory evaluation. The hardness of aged sheets significantly increased as a function of time, except at 30 °C ageing. Examination of cut surfaces of fresh sheets revealed a network formation, but the cut surfaces became smoother with ageing. Room-temperature ageing produced a rougher surface than did 0 °C ageing. These results indicate that low-temperature ageing can accelerate retrogradation. Noodle sheets aged for 3 h at 0 °C produced optimal hardening; moreover, noodles from accelerated ageing had a textural quality similar to that of traditionally aged noodles. This research indicates that ageing at 0 °C allows the ageing period to be reduced from 12 to 3 h without a loss in noodle quality.     

Effect of storage at 0 °C on mantle proteins and functional properties of jumbo squid

Effect of iced storage of jumbo squid mantle with fin on gelling capacity and changes in protein fractions and functional properties of jumbo squid mantle protein during storage at 0 °C were assessed. Most values of texture variables in gels did not significantly change during storage. On average, they were: strength 65.07 ± 4.71 N; elasticity 68.14 ± 5.3%, fracturability 52.97 ± 1.28 N and cohesiveness 36.6 ± 0.1%. Protein solubility increased more than 40%. Whippability increased during storage for 16 days at 0 °C (81–162%), as did foam stability (73–94%). Results suggest that iced squid mantle protein is a suitable ingredient for food products where these functional properties are desirable. Muscle fibres of squid mantle undergo various changes during storage. At 0 °C, they are disrupted, whereas at −20 °C, they aggregate and develop empty spaces in the tissue.     

Enhancement of human fibroblast growth and other dermatological effects induced by cell extract from heat-shocked blue green alga (Cyanobacteria)

It has been known that high amounts of 'heat shock proteins (HSPs)' are produced under heat and other environmental stresses in cells. Recently, it was reported that HSP could also be accumulated in some dermal cells to protect the cellular proteins from damage caused by ultraviolet radiation. Here, the authors have focused on thermophilic cyanobacteria and the heat shock treatment. Thermophilic cyanobacteria are known to thrive under extreme environmental conditions, and produce distinctively high amounts of HSP when exposed to higher temperatures. We tested cell extract from heat-shocked cyanobacterial cells on a number of skin-related biological activities and found it significantly effective. The cyanobacterial cells, originally collected from a spa as hot as 55 °C, were cultivated in the laboratory at 50 °C and broken by a freeze-fracture method. The extract thus obtained had a superoxide dismutase (SOD)-like activity and inhibited lipid peroxide formation. We found that the extract obtained from the heat-shocked (at 63 °C) cells showed a much stronger SOD-like activity, while the inhibitory effect on lipid peroxide formation remained almost the same. Furthermore, the SOD-like activity could withstand heat up to 70 °C for as long as 1 h. Most remarkably, supplementing this heat-shocked extract strongly promoted the proliferation of human dermal fibroblast culture. Extracts from the cells grown at a regular temperature (50 °C) did not promote the proliferation of the fibroblasts. The heat-shocked extract was fractionated by ultrafiltration for further analysis. A fraction (molecular weight: 10 000–30 000) has shown the strongest activity so far. These results indicate that the heat-shocked cyanobacterial extract with its increased amounts of HSPs is a promising potent ingredient for anti-aging cosmetic materials.     

Gelation Behavior of Protein Isolates Extracted from 5 Cultivars of Pisum sativum L.

ABSTRACT: Protein isolates were extracted from 5 pea ( Pisum ) cultivars and their gelation behaviors were compared at pH 7.6. Gel formation and development was monitored via constant oscillation dynamic measurements. The standard heating and cooling rate was 1.0°/min, but samples were also heated at 0.5°C (and cooled at 1.0°C/min), and others were heated at 1.0°C/min and cooled slowly at 0.2°C/min. When heating more slowly, no changes in gel formation were detected for any of the cultivars. When cooling slowly, the cultivar Solara, with the highest legumin content, formed a stronger gel than all the other cultivars. It did the same when the thiol-blocking agent N -ethylmaleimide (NEM) was added to the system. This indicated that the strengthened gel system formed independently of any disulfide bonds formed by the legumin. The cultivars Supra and Classic formed stronger gels only when cooled slowly in the presence of NEM, and so disulfide bond formation in their gel systems was apparently a factor that prevented gel network strengthening. The cultivars Finale and Espace were unable to form strong and self-supporting gels. This was believed to be because of the repulsive forces on the α-subunits of vicilin, which were at their highest level in the cultivars Finale and Espace. The contribution of legumin to the pea protein isolate gels was shown to be cultivar specific and related to its disulfide bonding ability rather than the absolute amount of legumin protein present.     

Effect of Extraction pH and Temperature on Isoflavone and Saponin Partitioning and Profile During Soy Protein Isolate Production

ABSTRACT: Soy protein isolates (SPIs) are produced industrially using methods using various protein extraction temperatures and pH values. The effects of process temperature (25°C or 60°C) and pH (8.5, 9.5, or 10.5) on isoflavone and group B saponin extraction, partitioning, and profile during bench-scale SPI production were evaluated. Protein, isoflavone, and saponin extraction increased with increasing temperature and pH. Substantial quantities of isoflavones and saponins remained in the insoluble fraction waste stream. Isoflavones were also lost to the whey waste stream, whereas saponins were not detected in the whey. Neutralization of SPI samples at the time of analytical extraction increased measured isoflavone concentrations for the pH 8.5 process extraction treatments, whereas neutralization substantially increased measured saponin concentrations in SPIs for all process extraction treatments. Malonylglucoside isoflavones were primarily converted to β-glucoside forms as temperature and pH were increased, and these conditions caused conversion of αg, βg, and βa saponins to saponin V, I, and II forms, respectively. Analytical extraction pH should receive careful consideration when analyzing soy matrices for isoflavones and saponins.     

Hot air drying of yacon (Smallanthus sonchifolius) and its effect on sugar concentrations

This work aimed to experimentally study the drying behaviour of yacon tubers with and without steam blanching. Drying was carried out for 5 h and 30 min in a forced air dryer at 50 °C, 60 °C and 70 °C. The results indicated that the shortest drying time was obtained at 70 °C for blanched samples, and that the equilibrium water activity values were significantly lower for the blanched samples at all temperatures. The yacon dried without prior blanching showed lowest concentrations of reducing sugars when dried at 70 °C, significantly lower than those dried at 50 °C and 60 °C. This indicates hydrolysis of the fructo-oligosaccharides at 70 °C, a fact verified by the significant increase in reducing sugars content from 36.65 ± 0.54–44.10 ± 0.96% and reduction in the non-reducing sugars from 31.62 ± 0.55–26.18 ± 0.29%.     

Rennin-like milk coagulant enzyme produced by a local isolate of Mucor

Among 20 isolates of Mucor isolated from various environments in Jordan and found to produce a rennin-like acid protease, known as Mucor rennin-like enzyme (MRE), Mucor J20 was found to produce the highest level of MRE. The optimum incubation conditions for enzyme production in a fortified wheat bran mixture using solid-state fermentation were 3–4 days at 30°C. The highest MRE activity (185–200 rennin units or RU) was produced in a medium containing wheat bran and lentil straw (1 : 1 w/w) moistened with whey, and incubated in clay pots at 30°C for 4 days. A slightly lower activity value (178 RU) was found when using a mineral salt solution or distilled water instead of whey, or when using wheat bran alone with whey. At pH 4, the MRE retained its complete activity (100%) for 6 weeks at 5°C and 10°C, and for 3 and 2 weeks at 20°C and 30°C, respectively. After heating at 60°C for 10 min, the enzyme lost its activity at all pH levels used (pH 2–8). The crude extract of MRE was successfully applied in the manufacture of a cheese curd.     

Proteins recovered from milks heated at alkaline pH values

Approximately 95% of available nitrogen can be precipitated from milk on adjustment to pH 4.6 after heating at 90°C × 15 minutes at its natural pH and pH 7.5, while 89% can be precipitated after heating at pH 10.0 at 60°C × 3 minutes. Non-recovered protein includes some serum albumin, β-lactoglobulin, α-lactalbumin and proteose peptones. Protein isolates precipitated from milk heated at pH >7.0 are more soluble in the pH range 6.0–7.0 than those precipitated from milk heated at its natural pH. Whey proteins complex onto the casein micelles after heating milk at its natural pH, while on heating at pH >7.0 whey proteins appear to interact with k-casein in the serum phase. When N-ethylmaleimide is present in milk during heating the percentage protein recovered on pH 4.6 precipitation is decreased, confirming that disulphide linkage is involved in complex formation. However, addition of β-mercaptoethanol to recovered isolates did not result in dissociation of the casein/whey protein complex, suggesting that forces other than disulphide bonding are also involved in maintaining the complex.     

Technological and spoiling characteristics of the yeast microflora isolated from Bella Di Cerignola table olives

This study focused to investigate the technological significance and the spoiling impact of diverse yeast strains, isolated from 'Bella di Cerignola' Italian table olives. Sixty-four isolates (belonging mainly to the species Candida famata and C. guilliermondii ) were studied to assess their growth at different temperatures (15, 25 and 37 °C), pHs (4.0, 5.0 and 9.5) and NaCl concentrations (0–10.0%) in lab medium. Their pectolytic, xylanolytic, lipolytic and catalase activities were also evaluated. Most of the yeasts showed a moderate pectolytic activity and were able to grow at pH 9.5 after 120 h of incubation. Salt and temperature were the most important environmental variables affecting yeast growth, which could exert a strong selective pressure on yeast population. Candida guilliermondii appeared more resistant to high salt concentrations, whereas C. famata was able to grow at 15 °C.     

Cooked and brined shrimps packed in a modified atmosphere have a shelf-life of >7 months at 0 °C, but spoil in 4–6 days at 25 °C

Summary Spoilage and safety of cooked, brined and modified atmosphere packed shrimps were studied at 0, 5, 8, 15 and 25 °C. Shrimps from two sources, cold and warm waters, were brined in a sodium–chloride brine containing benzoic, citric and sorbic acids. Shelf-life was above 7 months at 0 °C but only 4–6 days at 25 °C. Apparent activation energy for the effect of temperature on shelf-life was > 100 kJ mol^-1. This pronounced effect of temperature was explained by changes in spoilage microflora at different storage temperatures. Simple and empirical mathematical models for rates of spoilage were developed for the prediction of shelf-life at different temperatures. To evaluate safety, products were challenged with Listeria monocytogenes and spores of Clostridium botulinum . Above 5 °C growth responses of L. monocytogenes followed the square root model with a T_min-value of +0.2 °C. Cl. botulinum produced toxin at the time of spoilage at 25 °C but only in shrimps with < 3% water-phase salt.     

Combined effects of hydrostatic pressure, temperature, and pH on the inactivation of spores of Clostridium perfringens type A and Clostridium sporogenes in buffer solutions

ABSTRACT:  To develop a spore inactivation strategy, the effect of 15-min hydrostatic pressure treatments (550 and 650 MPa) at 55 and 75 °C in citric acid buffer (4.75 and 6.5 pH) on spores of 5 isolates of Clostridium perfringens type A carrying the gene that encodes the C. perfringens enterotoxin ( cpe ) on the chromosome (C- cpe ), 4 isolates carrying the cpe gene on a plasmid (P- cpe ), and 2 strains of C. sporogenes were investigated. Treatments at 650 MPa, 75 °C and pH 6.5 were moderately effective against spores of P- cpe (approximately 3.7 decimal reduction, DR) and C. sporogenes (approximately 2.1 DR) but not for C- cpe (approximately 1.0 DR) spores. Treatments at pH 4.75 were moderately effective against spores of P- cpe (approximately 3.2 DR) and C. sporogenes (approximately 2.5 DR) but not of C- cpe (approximately 1.2 DR) when combined with 550 MPa at 75 °C. However, when pressure was raised to 650 MPa under the same conditions, high inactivation of P- cpe (approximately 5.1 DR) and C. sporogenes (approximately 5.8 DR) spores and moderate inactivation of C- cpe (approximately 2.8 DR) spores were observed. Further advances in high-pressure treatment strategies to inactivate spores of cpe -positive C. perfringens type A and C. sporogenes more efficiently are needed.     

Storage stability of traditional Tunisian butter oil produced from spontaneous fermentation of cow's milk

Physicochemical characteristics of traditional Tunisian butter (TTB) and thermal stability of the butter oil were studied. Thermal stability of samples was estimated by using the accelerated shelf life testing method. Effect of heating on some quality characteristics of traditional Tunisian butter oil (TTBO) was investigated and compared at different temperatures (60°C, 100°C and 130°C). Induction period of sample heated at 60°C was important compared to that at 100°C and 130°C. This result may indicate the sensitivity of TTBO to elevated temperature. Absorption at 232 and 270 nm, acidity and PV increased rapidly after reaching the oxidation induction time. The temperature had a significant effect on the formation of oxidation products in traditional butter oil (TTBO). Fatty acid composition of TTBO was also changed after heating. This may explain the observed modification on some quality characteristics of TTBO such as viscosity, hardness, cohesiveness and colour. As a consequence, heat treatment produced alterations in the oxidative status of the butter oil that could affect the shelf life.     

Determination of optimum hazelnut roasting conditions

The objective of this study was to test the hypothesis that the roasting conditions used for hazelnuts, such as the air temperature, air velocity and roasting time (independent variables), could be optimized by using Response Surface Methodology. Effects of independent variables on sensory and physical characteristics were determined. A consumer test was used to determine the acceptable samples. Very dark and very light roasted samples, corresponding to 165 °C, 3 m/s, 25 min and 125 °C, 1 m/s, 15 min process conditions, respectively, were unacceptable. Superimposed contour plots were used to determine the values of independent variables and these showed the process conditions where all product characteristics were acceptable to consumers. At low velocity (0.3 m/s), acceptable products were produced at about 165–179 °C for 20–25 min. When air velocity increased, air temperature shifted to lower temperatures. Samples roasted at 145 °C, 2 m/s, 28 min, 165 °C, 1 m/s, 25 min and 145 °C, 3.7 m/s, 20 min produced the most acceptable products. The sample roasted at 165 °C, 1 m/s, 25 min required the least air velocity and was the most economical in terms of energy consumed among the samples rated most acceptable by consumers.     

REVERSIBLE GELATION OF WHEY PROTEINS: MELTING, THERMODYNAMICS AND VISCOELASTIC BEHAVIOR

Whey protein isolates formed reversible gels following heating at 90°C for 15 min under certain conditions i.e., pH 6.5 to 8.5 with protein concentration of 9.0–10.5%. The melting temperatures of the gels formed at pH 8.0 ranged from 24.5°C to 57.8°C. The maximum enthalpy of formation (ΔH_f) was –858 call mole of crosslinks. A maximum storage modulus (G') of 240 dynes/cm² was obtained following holding for 7 h at 8°C.     

Structural Characterization of Amaranth Protein Gels

ABSTRACT: Gelation capacity of a native amaranth protein isolate was studied. Structural properties of gels prepared at different protein concentration and heating conditions were analyzed. Proteins present in amaranth isolates obtained by water extraction at pH 9.0 and subsequent isoelectric precipitation are able to form gels of yellowish appearance. Gel color intensity increased while luminosity decreased with increasing protein concentrations. High protein concentration allowed the formation of matrices with high water-holding capacity. In addition, increasing the heating temperature resulted in gels of high luminosity and low water-holding capacity. The increase of protein concentration (10% to 20% w/v) as well as the increase of heating temperature (70°C to 95°C) and heating time (10 to 30 min) resulted in the formation of a more ordered matrix with smaller pores, mainly stabilized by disulfide bonds and, at a lower extent, by noncovalent interactions (specially hydrogen bonds and hydrophobic interactions). Both amaranth globulin (11S globulin and P globulin) participated in gel structure via high-molecular-weight aggregates (>100 kD). Gel structure was stabilized via noncovalent bonds by monomer species of 42 kD and those of molecular mass lower than 20 kD localized in the interstitial spaces of gel matrix.     

Effect of dry heat on the in vitro digestibility and trypsin inhibitor activity of chickpea flour

The effect of a dry heat treatment on trypsin inhibitors, protein quality and molecular weight of products obtained from enzymatic hydrolysis of chickpea flours was analysed in order to use chickpeas as food protein hydrolysates. Chickpea flour obtained from dehusked seeds was processed under different conditions, either by heating or enzymatic treatment. Heat treatment at 140 °C for varying times (1–24 h) inactivated trypsin inhibitors and facilitated enzymatic treatment but showed an unacceptable loss in the nutritional quality of the protein for heating times longer than 6 h. Enzymatic treatment with a commercial protease, Alcalase 0.6L, at pH 8 and 50 °C, increased the protein nutritional value of the chickpea by breaking the protein chains into shorter peptide chains more suitable to human nutrition.     

Thermal syneresis affected by heating schedule and moisture level in surimi gels

ABSTRACT:  The extent of thermal syneresis in protein gelation is indicative of thermal and freeze-thaw stability as well as the network integrity of a protein gel. Thermal syneresis in Alaska pollock surimi gels was examined under different heating schedules (40 °C/20 min to 90  °C/30 min, 60 °C/20 min to 90 °C/30 min, and 90 °C/20 min to 90 °C/20 min) at varying moisture levels (80%, 82%, and 84%). The extent of syneresis and gel firming was monitored by centrifugation expressible moisture and penetration force, respectively. The occurrence of 2 distinct peaks as a function of time for both thermal syneresis and gel firming suggests that a multistage aggregation is involved in the formation of gel network. All syneresis preceded gel firming upon protein aggregation. Increasing the moisture content in the gel delayed the 2nd stage of protein aggregation. The 60 °C/20 min preheating followed by 90 °C/30 min postheating resulted in significantly greater thermal syneresis and gel weakening compared to 40 and 90 °C preheating. Changes of gel structure clearly reflected thermal syneresis when the size of water pores became smaller with initiation of network formation and progressively larger upon further heating. Thermal syneresis history during protein gelation can be used to predict thermal and freeze-thaw stability.     

Growth and associated enzymic activity of spoilage bacteria in pasteurized double cream

Differences were observed in the proportions of isolates obtained from stored cream from the three major producers in the south of Scotland. It was shown that the incidence ofBacillus spp. was higher during storage at 10°C than at 6°C and was also higher in creams during the summer and autumn months . Pseudomonas spp. were the predominating organisms in stored creams, and the majority of isolates obtained were capable of degrading both milk fat and protein .     

Aerobic spore-forming bacteria in bulk raw milk: factors influencing the numbers of psychrotrophic, mesophilic and thermophilic Bacillus spores

Psychrotrophic, mesophilic and thermophilic spore concentrations of Bacillus spp. were determined on a weekly basis in bulk raw milk samples obtained from a central processing facility, over one calendar year. These data were correlated with concentrations of metal ions, free amino acids and somatic cell counts obtained from the same samples, as well as local meteorological mean temperature and relative humidity measurements relating to the same test period. A heat treatment of 80°C for 20 min followed by the addition of L-alanine to the milk at 0.1% w/v and incubation at 55°C for 7 days gave optimal recovery conditions for thermophilic spores. Free amino acids, metal ions, somatic cell counts, temperature, and relative humidity measurements were each significantly correlated with the recovery of spores of Bacillus spp. from bulk raw milk, although no single factor was shown to demonstrate a consistent effect with the psychrotrophic, mesophilic and thermophilic spore groups studied.     

Texture of rehydrated dried bell peppers modified by low-temperature blanching and calcium addition

Diced green bell pepper was blanched twice, once at 51–79 °C for 19–61 min, and once at 95 °C for 3 min, and dried. The firmness of rehydrated samples was measured by puncture, and optimum conditions assessed by response surface methodology. The optimized model showed that, blanching at 65 °C for 49 min gave a 64% increase in puncture force over the control. The optimum temperature was used to evaluate the effect of adding CaCl₂. The dices were blanched twice, once at 65 °C for 3 min in either 0 or 4% CaCl₂, secondly in either 0 or 2% CaCl₂ solution at 95 °C for 3 min. In the second case the dices had been held at room temperature for 0–30 min before treatment. Adding CaCl₂ increased puncture force significantly ( P  ≤ 0.05). The best results, those which gave greatest firmness, were obtained by blanching at 65 °C for 3 min in 4% CaCl₂, holding for 16 min after blanching, followed by a secondary blanching at 95 °C in 2% CaCl₂.