The development of a goat's milk yogurt

This study sought to establish conditions suitable for a small‐scale yogurt process using goat's milk and to examine the physicochemical properties (pH, titratable acidity, solids‐not‐fat (SNF), viscosity, texture) and organoleptic acceptability (preference by Filipino panellists) of the resultant product. Goat's milk was concentrated by heating (80 °C, 1 h), which resulted in an increase in SNF from 85 to 110 g kg^?1. To further improve the curd of goat's milk yogurt, two hydrocolloids were used: carrageenan (1.5 and 3 g l^?1) and pectin (50 g l^?1). The addition of dehydrated pineapple and banana cubes (50 and 100 g l^?1) in a sundae‐style formulation increased the SNF by an additional 2.5% and produced a curd that was firmer than the control, plain set yogurt. The use of carrageenan appeared to be a convenient way of controlling product viscosity. In terms of product preference and firmness the fruit‐flavoured sundae‐style yogurts were ranked higher by sensory panellists. Copyright © 2005 Society of Chemical Industry     

The effects of heating and chemical treatment on the haem and non-haem iron content of heat-induced porcine blood curd

The effect of heating temperature (40–80°C), time (0–50 min), additions of ascorbic acid (0–5 g litre^?1) and sodium nitrite (0–200 mg litre^?1) on total, non-haem and haem iron of heat-induced porcine blood curd (a famous edible blood food in Taiwan) was investigated. The results show that non-haem iron content increased significantly (P < 0.05) when heated at above 55°C and was enhanced linearly (r = 0.96) with heating time at 80°C, while haem iron decreased relatively. In addition, a non-haem iron increase was observed in ascorbic acid, the maximum found with treatment at 4 g litre^?1. On the contrary, haem iron content increased with the presence of sodium nitrite and there was a significant change with addition above 50 mg litre^?1.     

Production and characterization of milk-clotting enzyme from <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> JNU002 by submerged fermentation

Milk-clotting enzymes produced by microorganisms have been developed to replace calf rennet, yet the enzymatic level and the ratio of milk-clotting activity to proteolytic activity still need further improvement. This work described a strain Bacillus amyloliquefaciens JNU002 that screened from wheat bran that has a promising characterization. After optimization, B. amyloliquefaciens JNU002 showed a high milk-clotting activity (4969 SU/mL) and low proteolytic activity (4.02 U/mL) at 48 h with an inoculum size of 0.2% (v/v) at initial pH 6.0 in 15-L bioreactor. After purification, the purified enzyme gave a single protein band on SDS–PAGE, corresponding to 28 kDa. The purified enzyme showed a high ratio (2,575) of milk-clotting activity to proteolytic activity at 35 °C, and the ratio would be even higher (22,992) at 70 °C. The milk-clotting reaction and proteolytic reaction were prevented at 75 °C. This enzyme was stable at pH 4–6 and below 40 °C, and this was convenient for storage and transportation.     

Development of peanut milk–based fermented curd

Fermented milk product (Indian curd) was developed by using peanut milk. The level of incubation period (IP), skimmed milk powder (SMP), carboxymethyl cellulose (CMC) was optimised using response surface methodology (RSM). Central composite rotatable design was used with three independent variables i.e. IP (16–20 h), SMP (3–5%) and CMC (0.1–0.3%). SMP had significant (P ≤ 0.05) positive effect on overall acceptability (OAA) of curd because of increase in the total solids that ultimately increased firmness of the curd. CMC was found effective in reducing the synersis of curd samples. The developed curd samples had moisture 84.8 ± 0.28%, protein 3.2 ± 0.12%, fat 3.5 ± 0.10%, ash 0.5 ± 0.05%, carbohydrate 8.0% (wb), peak viscosity 291.4 ± 3.52 cP, firmness 1.3 ± 0.15 N, synersis 32.1 ± 0.2 mL 100 g^?1 and acidity (as % lactic acid) 0.58 ± 0.02. It had OAA score of 7.8 ± 0.2 on nine‐point hedonic scale. Based on compromise optimisation, the conditions recommended were IP as 18 h, SMP, 4.24% and CMC, 0.19% for making peanut milk–based fermented curd with 83.4% desirability.     

Ripening temperature affects the content and distribution of isoflavones in sufu,a fermented soybean curd

Sufu, a fermented soybean curd, was prepared by ripening the salted tofu cubes in the Aspergillus oryzae‐fermented rice–soybean koji mash at 25, 35 or 45 °C for a period of 16 days. It showed that the 16‐day ripened sufu contains less total isoflavone content (629.29–739.68 μg g^?1 dried matter) than the salted tofu before ripening (942.59 μg g^?1 dried matter). Regardless of ripening temperature, ripening causes a major reduction in the content of β‐glucoside and malonylglucoside isoflavones along with a significant increase of aglycone isoflavone content. These changes were enhanced as the ripening period extended. Among the various treatments examined, sufu ripened at 45 °C showed the greatest increase in aglycone content coupled with the greatest decrease in malonylglucosides. The distribution of malonylglucosides decreased from an initial 40.32% in the tofu cube to 9.78% after 16 days of ripening at 45 °C. Meanwhile, the distribution of aglycone increased from 13.17% to 39.88%.     

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at −2 °C min⁻¹. The effects of variation in levels of temperature (57.93–72.07 °C) and time (15.86–44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box–Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60–70 °C) and time (20–40 min) in the first blanching step and steaming temperature (112–122 °C) and time (1–3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22 °C and 29.37 min before freezing and 64.39 °C and 28.02 min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues. © 1999 Society of Chemical Industry     

Milk Curdling by Rennet under High Pressure

The effect of pressure on milk curd formation initiated by rennet was studied under high pressures. The milk used was a 20% solution of skim milk powder in 0.02M CaCl₂. After holding the milk with rennet at 35°C for given periods under high pressure, up to 1300 kglcm², the extent of proteolytic digestion and the curd tension were measured under atmospheric pressure. Rennet and milk protein were not denatured by pressure under the experimental conditions used. The primary phase reaction of milk curdling by rennet (hydrolysis of casein) was not affected by compression. The secondary phase reaction (core formation of casein micelle aggregates) was delayed under high pressure and the tertiary phase reaction (milk curd formation) was accelerated.     

Biochemical and rheological characterization of a protease from fruits of Withania coagulans with a milk-clotting activity

A protease from Withania coagulans fruits was evaluated for milk-clotting properties. The optimum temperature and pH for enzyme activity were 70°C and 4, respectively. The protease also exhibited an excellent thermal stability at 60°C for 30 min. Fractional precipitation using ammonium sulfate showed that the 40–50% fraction (F5) possessed the highest milk-clotting activity. The F5 fraction showed a Mw band of 66 kDa by SDS-PAGE. Gel formation was monitored using low amplitude oscillatory rheology at different temperatures. An Arrhenius plot was used to describe the temperature dependence of the gelation rate parameter. Time sweep testing showed that an increase in temperature was accompanied by a decrease in the gelation onset time, a higher gel formation rate, and higher values for final gel strength. W.coagulans fruits have potential for use as a rennet substitute.     

Expression and characterization of β-1,3-1,4-glucanase of Aspergillus usamii in Escherichia coli and its application in sourdough bread making

A β-1,3-1,4-glucanase gene (Auglu12A) from Aspergillus usamii was successfully expressed in Escherichia coli BL21(DE3). The recombinant enzyme, reAuglu12A was efficiently purified using the one-step nickel-nitrilotriacetic acid affinity chromatography. The specific activity of reAuglu12A was 694.8 U/mg, with an optimal temperature of 55°C and pH of 5.0. The reAuglu12A exhibited stability at temperatures up to 60°C and within the pH range of 4.0–5.5. The reAuglu12A hydrolytic activity was increased in the presence of metal ions, especially K⁺ and Na⁺, whereas it exhibited a K_m and V_max of 8.35 mg/mL and 1254.02 µmol/min/mg, respectively, toward barley β-glucan at pH 5.0 and 55°C. The addition of reAuglu12A significantly increased the specific volume (p < 0.05) and reduced crumb firmness and chewiness (p < 0.05) of wheat–barley sourdough bread during a 7-day storage period compared to the control. Overall, the quality of wheat–barley sourdough bread was improved after incorporation of reAuglu12A (especially at 3000 U/300 g). These changes were attributed to the synergistic effect of acidification by sourdough and its metabolites which provided a conducive environment for the optimal action of reAuglu12A in the degradation of β-glucans of barley flour in sourdough. This stabilized the dough structure, thereby enhancing the quality, texture, and shelf life of the bread. These findings suggest that reAuglu12A holds promise as a candidate for β-glucanase application in the baking industry.     

Survival of probiotic bifidobacteria in buffalo curd and their effect on sensory properties

The feasibility of incorporating Bifidobacterium longum NCTC11818 in buffalo curd to produce a probiotic product was investigated. Fermentation at tropical ambient temperature (29 ± 2 °C), two storage temperatures (29 ± 2 °C and 4 ± 2 °C), and in three packaging materials (clay pots, plastic cups, and glass bottles) was investigated. Bifidobacteria survived for 3 days above the required population level of 10⁶ CFU g^?1 in buffalo curd packed in clay pots at 29 ± 2 °C. They did not persist at acceptable levels over the 4‐day shelf life because of the combined effects of temperature, acidity, and redox potential. Chill storage slows post‐fermentation acidification and prolongs bifidobacterial viability while packaging materials, which present a greater barrier to oxygen, had a similar effect. The results indicated that bifidobacteria could be successfully incorporated into buffalo curd to give a product which has improved acceptability. Probiotic buffalo curd, when compared to uninoculated curd, had significantly higher (P < 0.05) sensory scores for properties such as taste and mouth‐feel resulting in a significantly higher (P < 0.001) overall acceptability.     

Effect of Air Temperature on Drying Kinetics,Vitamin C,Antioxidant Activity,Total Phenolic Content,Non-enzymatic Browning and Firmness of Blueberries Variety O´Neil

Effect of air temperature on drying kinetics, vitamin C, antioxidant capacity, total phenolic content (TPC), colour due to non-enzymatic browning (NEB) and firmness during drying of blueberries was studied. Drying curves were satisfactorily simulated with the Weibull model at 50, 60, 70, 80 and 90°C. The scale parameter (β) decreased as air temperature increased and an activation energy value of 57.85 kJ mol⁻¹ was found. Important losses of vitamin C were reported during drying for all the working temperatures (p < 0.05). Although TPC decreased as air-drying temperature increased (p < 0.05) in comparison to its initial value, the dehydration at high temperatures (e.g., 90°C) presented high values for these antioxidant components. Discoloration due to NEB reaction was observed at all the working temperatures showing a maximum value at 90°C (p < 0.05). The radical scavenging activity showed higher antioxidant activity at high temperatures (80 and 90°C) than at low temperatures (50, 60 and 70°C) (p < 0.05). A tissue firmness reduction was observed with increasing temperature (p < 0.05).     

Accumulation of lignin and involvement of enzymes in bamboo shoot during storage

Fresh bamboo (Phyllostachys praecox f. prevernalis.) shoots were harvested, and the changes of firmness, electrical conductivity (EC), respiration rate, ethylene production, total sugars (TS), reducing sugars (RS), lignin and cellulose content and the activity of phenylalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase POD were investigated during storage at 2 or 20°C for 30 or 12 days, respectively. EC increased quickly, with a more rapid rate at higher temperature, but it increased sharply after 24 days at 2°C. Respiration rate increased slowly at 20°C, while at low temperature (2°C) respiration rate and ethylene production significantly decreased. There was a quickly decrease in TS content at 20°C. Shoot firmness, lignin and cellulose increased and accelerated by higher storage temperature during storage at 2 or 20°C. Shoots firmness showed a positive correlation with accumulation of lignin and cellulose in the flesh. Among the enzymes associated with lignin synthesis, PAL and CAD activity showed a persistent rise over the whole 12 days, while POD activity increased rapidly within 6 days during storage at 20°C, followed by a slowly decrease. Accumulation of lignin in flesh tissue was also positively correlated to activity of PAL, CAD and POD. Our results suggest that the increase in firmness of bamboo shoots during storage is a consequence of tissue lignification, a process associated with increases in PAL, CAD and POD activity.     

Laundry detergent-stable lipase from Pacific white shrimp (Litopenaeus vannamei) hepatopancreas: Effect of extraction media and biochemical characterization

Extraction and biochemical properties of a new lipase from the hepatopancreas of Pacific white shrimp were studied. Recovery of the hepatopancreas powder with 50 mM Tris-HCl, pH 7.0 containing 0.2% (v/v) Brij35 gave a higher recovery of lipase activity than other extractants tested (p < 0.05). The optimal pH and temperature for lipase activity were 8.5 and 60°C, respectively, when p-nitrophenyl palmitate was used as a substrate. The enzyme was stable to heat treatment up to 40°C and over a pH range of 7.0–10.0 for 30–120 min. Lipase activities continuously decreased as the sodium deoxycholate (NaDC) concentration increased, but activities increased as NaCl concentration increased up to 3.0 M. Hydrolytic activity was enhanced by NaN₃, but strongly inhibited by Hg²⁺, Cu²⁺, Al³⁺, and phenylmethanesulfonyl fluoride. The lipase was evaluated as highly stable against surfactants (Tween 20, Tween 80, Triton X-100, and gum arabic). However, the enzyme was unstable against sodium dodecyl sulphate. Stability of the lipase with commercial liquid and solid detergents (Attack^®, Bres^®, Omo^®, and Pao^®) was also investigated. The lipase exhibited substantial stability and compatibility with tested commercial liquid and solid laundry detergents for 30–60 min. The overall properties of the lipase from Pacific white shrimp hepatopancreas, thus leading us to propose that it is an excellent candidate for use as biocatalysts for better detergent formulation.     

Flow Properties, Firmness and Stability of Double Cream Cheese Containing Whey Protein Concentrate

As estimated on-line, the viscosity after cooling of double cream cheese curd containing heat-denatured WPC (DCC +) increased from 1.4 Pa.s to 1.7 Pa.s when cooled to the range of 45°C to 24°C, and then decreased from 1.7 Pa.s to 1.0 Pa.s when cooled from 24°C to 15°C. The viscosity of DCC^- (without heat-denatured WPC) increased from 1.5 Pa.s to 2.2 Pa.s at temperature shift from 40°C to 15.5°C. The firmness of stored DCC + and DCC^-, respectively, decreased from 15.1N to 6.5N when cooled to temperatures from 45°C to 15°C, and from 17.9N to 9.9N when cooled from 40°C to 15.5°C, as recorded by cone penetrometry. The structure of DCC+ cooled to 15°C collapsed after penetrometry, and DCC+ cooled to 20°C destabilized during shearing in coaxial cylinder rheometer. A new phase in DCC+ based on milk fat globules liberated by cluster disruption may be the cause of the structural and textural instability.     

Response surface methodology modeling of protein concentration,coagulum cut size,and set temperature on curd moisture loss kinetics during curd stirring

The effects of the independent variables protein concentration (4–6%), coagulum cut size (6–18 mm³), and coagulation temperature (28–36°C) on curd moisture loss during in-vat stirring were investigated using response surface methodology. Milk (14 kg) in a cheese vat was rennet coagulated, cut, and stirred as per semihard cheesemaking conditions. During stirring, the moisture content of curd samples was determined every 10 min between 5 and 115 min after cutting. The moisture loss kinetics of curds cut to 6 mm³ followed a logarithmic trend, but the moisture loss of curds from larger cut sizes, 12 or 18 mm³, showed a linear trend. Response surface modeling showed that curd moisture level was positively correlated with cut size and negatively correlated with milk protein level. However, coagulation temperature had a significant negative effect on curd moisture up to 45 min of stirring but not after 55 min (i.e., after cooking). It was shown that curds set at the lower temperature had a slower syneresis rate during the initial stirring compared with curds set at a higher temperature, which could be accelerated by reducing the cut size. This study shows that keeping a fixed cut size at increasing protein concentration decreased the level of curd moisture at a given time during stirring. Therefore, to obtain a uniform curd moisture content at a given stirring time at increasing protein levels, an increased coagulum cut size is required. It was also clear that breakage of the larger curd particles during initial stirring can also significantly influence the curd moisture loss kinetics. Both transmission and scanning electron micrographs of cooked curds (i.e., after 45 min of stirring) showed that the casein micelles were fused at a higher degree in curds coagulated at 36°C compared with 28°C, which confirmed that coagulation temperature causes a marked change in curd microstructure during the earlier stages of stirring. The present study showed the dynamics of curd moisture content during stirring when using protein-concentrated milk at various set temperatures and cut sizes. This provides the basis for achieving a desired curd moisture loss during cheese manufacture using protein-concentrated milk as a means of reducing the effect of seasonal variation in milk for cheesemaking.     

Purification and characterization of Bacillus subtilis milk-clotting enzyme from Tibet Plateau and its potential use in yak dairy industry

A milk-clotting enzyme named YS-1 was purified from a Bacillus subtilis (B. subtilis) YB-3, which we have isolated from Tibetan Plateau, Gansu, China. The enzyme YS-1 was identified as a metalloproteinase. SDS-PAGE and MALDI-TOF-MS analysis of the purified enzyme gave a molecular weight of 42 kDa. YS-1 was stable over a wide range of temperature from 20 to 60 °C. Purified YS-1 was also active over a wide range of pH from 5.0 to 9.0. It can be activated by Ca²⁺ and Al³⁺ but inhibited by Zn²⁺, Fe²⁺ and Cu²⁺. The milk-clotting enzyme YS-1 exhibited high specificity to substrate β-casein and yak milk casein and led to a 75% more rapid coagulation of yak milk than cow milk, due to high β-casein content in yak milk. Together, our findings confirmed that the enzyme YS-1 has a potential to be used in yak cheese industry.     

Changes in selected quality characteristics of minimally processed carambola (Averrhoa carambola L.) when treated with ascorbic acid

‘B 10’ carambola of ripening stage (RS) 3 and 4 were minimally processed (MP) and then dipped in 0, 15 and 30 mg L^?1 ascorbic acid (AA). The 1‐cm‐thick slices were then dried, packed into cling‐wrapped‐foam tray and stored at 7 °C for 0, 3 and 5 days. Skin colour (L*, C* and h°), flesh firmness, soluble solids concentration, vitamin C content, titratable acidity, pH, degree of browning, polyphenoloxidase (PPO) activity and sensory attributes of MP carambola treated with AA were determined. AA treatment had significant effect in decreasing cut surface browning degree but no significant effect on all the selected quality characteristics of the MP carambola. In the sensory evaluation, flesh colour, sweetness, flavour and overall taste were significantly affected by AA treatment especially at 15 mg L^?1. The RS of fruit significantly affected skin colour (C* and h°), pH and sensory attributes of colour and flavour of the MP carambola. As storage day (SD) progressed, skin colour (C* and h°), flesh firmness and vitamin C content, cut surface browning, PPO activity and all the sensory attributes of MP carambola decreased significantly. Flesh firmness of the MP carambola was affected by the interaction between AA × SD. Sensory attributes of MP carambola were affected significantly by AA × RS. All the sensory attributes of MP carambola positively correlated to each other but negatively correlated with browning degree. PPO activity positively correlated with browning degree. Copyright © 2007 Society of Chemical Industry     

The linamarase of Leuconostoc mesenteroides: Production,isolation and some properties

Leuconostoc mesenteroides was found to produce highly active linamarase when linamarin was incorporated in its growth medium. The enzyme was isolated from the bacterium and partially purified using diethylaminoethyl (DEAE) cellulose. Its activity was measured spectrophotometrically using linamarin extract. This yielded 62.2 mg CN^? g^?1 of linamarin. A study of some of its properties showed it was active in the temperature range of -10 to +45°C, with an optimum at 29°2°C. Activity was observed over a wide pH range, 4.0–8.0, with optimum at 6.0–6.5. Its pH of stability was 5.5–7.5, while above pH 8.0 there was a rapid loss of activity. Incubating the enzyme at 50°C led to loss of over 90% of its activity within 18 min. The optimal substrate concentration was 0.15–0.20 ml^?1. Whereas above 0.25 mg ml^?1 there was no observable increase in activity, loss of activity became more pronounced below 0.10 mg ml^?1 of substrate.     

Optimization of the Process Parameters to Establish the Quality Attributes of DPPH Radical Scavenging Activity,Total Phenolic Content,and Total Flavonoid Content of Apple (Malus domestica) Honey Using Response Surface Methodology

The response surface methodology was used to study the combined effect of temperature (60 to 80°C), time (10 to 15 min), and pH (3 to 6) on the antioxidant activity (1,1-diphenyl-2-picrylhydrazyl-radical scavenging activity, total phenolic content, and total flavonoid content) of apple honey. Statistical analysis revealed that all the responses were significantly (p < 0.05) affected by independent process variables. 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, total phenolic content, and total flavonoid content increased with the increase in time and temperature due to the formation of browning pigments. The antioxidant properties of apple honey significantly (p < 0.05) decreased with increase in pH from 3 to 6. The thermal treatment of apple honey at 80°C was found to be more effective than at 70 and 60°C. The average increase in 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, total phenolic content, and total flavonoid content of raw apple honey due to combined effect of three process variables was 9.6% ± 1.9, 13.7 ± 2.5 mg gallic acid equivalent/100 g and 49.3 ± 3.3 mg quercetin/100 g, respectively. The results showed that the most desirable optimum conditions for temperature, time and pH for 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (92.39%), total phenolic content (133.55 mg gallic acid equivalent/100 g of honey), and total flavonoid content (25.82 mg quercetin/100 g of honey) were 80°C, 15 min and 3.01, respectively. The results demonstrated that thermal treatment significantly increased the antioxidant activity of apple honey.