Comparison of the rheology of mozzarella-type curd made from buffalo and cows’ milk

Curd rheology and calcium distribution in buffalo and cows’ milk, were compared at their natural pH and during acidification (pH 6.5–5.6). Buffalo milk displays a curd structure and rheology different from that of cows’ milk and the casein-bound calcium, as well as the contents of fat, protein and calcium, are also higher. Due to these higher amounts of casein-bound calcium, the overall curd strength with buffalo milk (as indicated by the dynamic moduli) was higher, at similar pH values, than those of equivalent gels produced from cows’ milk. The curd rheology was adversely affected at lower pH (5.8–5.6) in both of the milk types, due to the loss of casein-bound calcium from casein micelles. The degree of solubilisation of calcium in buffalo milk during acidification is quite different from that observed in cows’ milk with a lower proportion of the calcium being solubilised in the former. The maximum curd firmness was obtained at pH 6.0 in both milk types. For both species, these rheological and micellar changes were qualitatively the same but quantitatively different, due to the different milk compositions.     

The use of multi element profiling to differentiate between cowand buffalo milk

The multi element profile of milk from 12 cows and 6 water buffaloes was investigated, to establish whether dairy products derived from the two species could be distinguished. Multi-element data were obtained using ICP-MS. Following assessment against the team’s QA/QC criteria, or where the levels were below the LOD for the procedure, 16 elements (P, S, K, Ca, V, Cr, Mn, Fe, Co, Zn, Ga, Rb, Sr, Mo, Cs and Ba) were submitted for statistical analysis. Using linear discriminant analysis (LDA) it was possible to differentiate between milk from the two species, produced under identical environmental and animal husbandry conditions, on one farm. The sources of food and water available for consumption by the animals were also analysed and the results showed that there was no correlation between the elemental composition of the dietary components and the profiles observed in the milk.     

Effects of gelation temperature on Mozzarella-type curd made from buffalo and cows’ milk. 1: Rheology and microstructure

The rheology and microstructure of Mozzarella-type curds made from buffalo and cows’ milk were measured at gelation temperatures of 28, 34 and 39 °C after chymosin addition. The maximum curd strength (G′) was obtained at a gelation temperature of 34 °C in both types of bovine milk. The viscoelasticity (tan δ) of both curds was increased with increasing gelation temperature. The rennet coagulation time was reduced with increase of gelation temperature in both types of milk. Frequency sweep data (0.1–10Hz was recorded 90 min after chymosin addition, and both milk samples showed characteristics of weak viscoelastic gel systems. When both milk samples were subjected to shear stress to break the curd system at constant shear rate, 95 min after chymosin addition, the maximum yield stress was obtained at the gelation temperatures of 34 °C and 28 °C in buffalo and cows’ curd respectively. The cryo-SEM and CLSM techniques were used to observe the microstructure of Mozzarella-type curd. The porosity was measured using image J software. The cryo-SEM and CLSM micrographs showed that minimum porosity was observed at the gelation temperature of 34 °C in both types of milk. Buffalo curd showed minimum porosity at similar gelation temperature when compared to cows’ curd. This may be due to higher protein concentration in buffalo milk.     

Fortification of milk with plant extracts modifies the acidification and reducing capacities of yoghurt bacteria

The acidification and reducing capacities of yoghurt bacteria were evaluated in different plant extract‐enriched milk samples. The milk samples enriched with thyme and grape seed extracts exhibited the highest values of acidification capacity for Lactobacillus delbrueckii subsp. bulgaricus (LB) (0.0065 pH unit/min) and Streptococcus thermophilus (ST) (0.0068 pH unit/min). The highest values of reducing capacity were observed in thyme (?0.98 mV/min), grape (?1.92 mV/min) and green tea (?0.75 mV/min)‐enriched samples for LB, ST and mixed culture of LB + ST, respectively. The fortification of yoghurt with plant extracts modified the acidification and reducing activities of starters, thus changing the fermentation time and quality attributes of the product.     

The physico-chemical characteristics of extruded snacks enriched with tomato lycopene

Adding tomato derivatives to traditional starchy extruded snacks can improve their nutritional properties by adding lycopene and fibre; however the physico-chemical properties of these products must also be considered. Ingredients and extrusion parameters, including temperature, alter these properties, but their effect on lycopene content is not known. In this study, crisp low density extruded snacks were manufactured from corn, wheat and rice, with or without dried tomato skin or paste powder extruded at temperatures of 140, 160 or 180 °C. Lycopene content and the physico-chemical properties (expansion, density, hardness, colour parameters and percentage of moisture loss) of the extruded products were measured. Lycopene retention was higher in products containing tomato skin powder and significantly lower when wheat flour was used to make the snacks. Increases in the processing temperature improved the physico-chemical characteristics of the snacks but had no significant effect on lycopene retention (P > 0.05).     

Evaluation of the influence of arsenical livestock drinking waters on total arsenic levels in cow’s raw milk from Argentinean dairy farms

The concentrations of total arsenic in cow’s raw milk and in the livestock drinking water were determined and compared, in order to establish the influence of natural arsenic levels in groundwaters on the final presence of arsenic in milk production of the most important dairy region in Argentina. A dry ashing procedure was used for the mineralisation of the milk samples. The total arsenic concentrations were determined by flow injection hydride generation atomic absorption spectrometry (FI-HGAAS). The mineralised milk samples and well water samples were pre-reduced with concentrated HCl and KI–C₆H₈O₆ solutions. A volume of 500 μl of each solution of pre-treated sample was transported by a HCl 1.2 mol l⁻¹ carrier solution at a flow rate of 11 ml min⁻¹ and merged with a reducing NaBH₄ 0.2% (m/v) solution which flowed at 5.5 ml min⁻¹. The hydride generated in a reaction coil was transported to the detector with a N₂ flow of 100 ml min⁻¹. The recovery values of added concentrations at levels of 2.5 μg l⁻¹ and 5.0 μg l⁻¹ of arsenic in milk were 103 ± 8% and 102 ± 6% for n = 3, respectively. The accuracy of the method for the determination of total arsenic in water was checked by analysis of a certified sample NIST 1643d. Detection limits were 0.7 μg l⁻¹ and 0.6 μg l⁻¹ for milk and well water, respectively. The results showed a low biological transference level of arsenic to the cow milk from the drinking water ingestion.     

Physical properties of acid milk gels: Acidification rate significantly interacts with cross-linking and heat treatment of milk

Rheological properties and microstructure of acid milk gels largely depend on the pre-treatment of the milk, including heating and enzymatic modification of the gel-forming proteins. It was the aim of our study to investigate the impact of the acidification rate on gels which were produced from milk reconstituted from powder containing casein cross-linked by microbial transglutaminase (mTGase), and on gels which were produced from cross-linked raw milk. 3–7% Glucono-δ-lactone (GDL) was used as acidulant. Gel stiffness was determined by dynamic small-deformation rheometry and penetration experiments, and forced syneresis and gel permeability served as indicators for gel microstructure.     

The effects of silage feeding on some sensory and health attributes of cow’s milk: A review

Silage has been the prevailing type of preserved forage for cattle feeding in many countries. Carry-over of some components from silage to cow’s milk has been thus of concern. Silage is a richer source of available provitamins A, other carotenoids and tocopherols than hay due to higher losses of these compounds during forage field-drying and hay storage. Ensiled grasses and legume forages contain higher levels of carotenoids and tocopherols than maize silage. Numerous terpenes are carried-over to milk and cheeses from grazed multifloral pastures or from hay, while silages are a poorer source of these flavour-affecting compounds. Data on alcohols, acids, esters, aldehydes and ketones in silage and especially information on their carry-over to milk are insufficient. Milk can gain a bad smell from a stable atmosphere if silage, particularly of poor quality, is fed. Red clover silage feeding can cause considerable levels of estrogenic equol in milk. Deoxynivalenol and zearalenone are the main mycotoxins formed in silage. Their content is reduced by the activity of both some lactic acid bacteria in silage and rumen microflora. The excretion of the mycotoxins in milk is generally low. Silages can be a pool of the undesirable bacteria Bacillus cereus, Clostridium tyrobutyricum and Listeria monocytogenes. Milk contamination with these bacteria can be decreased by the prevention of silage deacidification following air access, and by improving the dairy farm environment, cow hygiene and by sanitary milk harvesting.     

Effect of age and gender on the processing characteristics of buffalo meat

Comparison of processing characteristics of meat from young male, spent male and spent female buffaloes was made to find the suitability of the meat for developing ready to eat meat products. Intensively reared young male buffalo meat showed higher moisture, collagen solubility, sarcomere length, myofibrillar fragmentation index and water holding capacity than meat from the other animals. A higher pH, total meat pigments, salt soluble protein, emulsifying capacity and lower collagen solubility were observed in spent male buffalo meat. Spent female buffalo meat had higher fat, total collagen, muscle fibre diameter and shear force value. Sensory evaluation of pressure cooked meat chunks indicated a marked toughness in spent male and female buffalo meat samples. These results suggest that young male buffalo meat is more suitable for processing in chunks and spent male and female buffalo meat is more suitable for processing in smaller particles.     

Influence of total solids contents of milk whey on the acidifying profile and viability of various lactic acid bacteria

The main objectives of the present study were (a) to study the effects of the different combinations of Lactobacillus delbrueckii subsp. bulgaricus (Lb), Lactobacillus acidophilus (La), Lactobacillus rhamnosus (Lr), and Bifidobacterium animalis subsp. lactis (Bl) in co-culture with Streptococcus thermophilus (St) on the rate of acid development in milk and milk-whey mixture, and (b) the effect of the level of the total solids of the different bases on the acidification profile and viability of potential health-promoting micro-organisms. The co-culture of St-Lr showed the lowest values V_max in all bases; while the co-culture St-Bl had high t_Vmax in milk and whey bases (12 and 10 g/100 g, respectively). Co-cultures St-La and St-Lb reached V_max at pH 5.5, while St-Lr and St-Bl at pH 5.91. Fermentation time to reach pH 4.5 was longer when St-Lr co-culture was used, while St-Lb had the lowest value. All the products had slight development of acid during the storage period, and lowest values were observed when the St-Bl co-culture was employed. Lb, Bl and St cultures had high counts at pH 4.5 in the three bases. The total solids affected the viability of Lb and La. The technological interest of these combinations is discussed in this article.     

Effects of gelation temperature on Mozzarella-type curd made from buffalo and cows' milk: 2. Curd yield, overall quality and casein fractions

The overall quality of Mozzarella-type curds made from buffalo and cows' milks were measured at gelation temperatures of 28, 34 and 39°C, and cutting times of 45, 60, 75 and 90min after chymosin addition. The curd yield and moisture content decreased with increasing gelation temperature, while whey fat losses increased. The effect of higher gelation temperature (39°C) was more pronounced in cows' milk than buffalo milk. This results in more fat losses and lower yields in both milk samples at a gelation temperature of 39°C. The minimum losses of fat and protein in rennet whey occurred at a gelation temperature of 34°C in both milk samples. The curd yield was higher in buffalo milk as compared to cows' milk. This is due to difference in total solids (fat and protein contents) of the two types of bovine milk. The different cutting times had a small effect on the yield and overall quality of curds made from both milk types. Curd moisture and loss tangent have a strong relationship with respect to effects of gelation temperature. Two different curd drainage methods (centrifugation and Buchner funnel filtration) were used to compare the final overall quality of Mozzarella-type curds made from both milk types. The α(s1) and β casein fractions were found to be in different proportions in the two milk types. The total- and casein bound-calcium were higher in buffalo milk than cows' milk. The total protein, casein and fat were also found to be higher in buffalo milk than cows' milk.     

广西水牛奶与荷斯坦牛奶工艺学特性比较

为了探索、比较广西水牛奶与荷斯坦牛奶的工艺学特性,对二者的缓冲容量、表面张力、粒度分布、稳定系数进行了比较分析。结果表明,广西水牛奶的缓冲容量和粒径分别是荷斯坦牛奶的1.1倍和2倍。在研究范围内,广西水牛奶在pH值为6.8时缓冲容量最大,温度50℃时表面张力最小,pH值为4.7时稳定系数最小;而荷斯坦牛奶在pH值为6.6时缓冲容量最大,温度为50℃时表面张力最小,pH值为4.6时稳定系数最小。广西水牛奶的粒径分布在91.28~458.7 nm之间,荷斯坦牛奶的粒径主要分布为91.28~190.1 nm之间,因此,认为两种牛奶的工艺学参数存在多方面的差异。     

Preparation and characteristics of lactic acid fermented cowpea milk

 Four Lactobacilli were isolated from both commercial cowmilk yoghurt ("Fan" yoghurt) and "wara", a West African soft cheese. They were identified as Lactobacillus acidophilus ("Fan" yoghurt), L. plantarum, L. brevis and unidentified Lactobacillus spp. ("wara"). L. acidophilus and L. plantarum were chosen as starter organisms for the production of a yoghurt-like product from cowpea milk. There was a decrease in the final pH and an increase in the titratable acidity of the cowpea milk samples at the end of the fermentation period. The crude protein, total ash, calcium, potassium and phosphorus values increased in the fermented cowpea milk, while a decrease was obtained for the lipid, moisture and crude fibre contents. A decreasing trend was noted in the phytic acid and trypsin inhibitor of the cowpea flour when processed into milk, followed by a further reduction at the end of fermentation. Consumer acceptability of the cowpea yoghurt varied, with preference being given to the banana and strawberry flavoured samples. Received: 10 June 1996 / Revised version: 17 September 1997     

Effects of continuous flow microwave treatment on chemical and microbiological characteristics of milk

Raw cows' and goats' milks were heated by microwave in a continuous flow unit up to temperatures ranging from 73.1 to 96.7°C. The effects of the heat treatments were estimated by measurements of lactose isomerization, protein denaturation, inactivation of alkaline phosphatase and peroxidase and the total bacterial count. Negative phosphatase tests and low bacterial counts, together with low degrees of whey protein denaturation, were achieved under several temperature/time combinations. The results indicate that continuous microwave processing may be an efficient and mild approach for the pasteurization of milk.     

Low temperature post-harvest storage of New Zealand Taewa (Maori potato): Effects on starch physico-chemical and functional characteristics

Fresh tubers from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro and Moemoe) and one modern potato cultivar (Nadine) of New Zealand, were stored at 4 °C and 80–90% relative humidity for six months after harvest. Starch was isolated from tubers after every three month period, and its physico-chemical and functional properties measured. Considerable changes in these properties occurred during storage. The extent of changes varied significantly from cultivar to cultivar. Starch swelling power, solubility and light transmittance decreased during tuber storage while a slight increase was observed in starch amylose content. The starch granule size distribution shifted to smaller granule size during tuber storage. Scanning electron micrographs showed degradation/erosion and pitting on the surfaces of many of the starch granules isolated from stored tubers. Transition temperatures and enthalpies of gelatinization of the starches increased somewhat during tuber storage, suggesting that changes in the stability of starch crystalline structures had occurred. Pasting, viscoelastic and texture profile analysis (TPA) characteristics of starch gels were found to have been influenced by tuber storage time for all the cultivars, but to the greatest extent for Nadine and Huakaroro. Gels made from starches from the stored tubers had a reduced tendency towards retrogradation as evidenced by the decrease in syneresis (%) during gel storage at 4 °C.     

西米淀粉的物化性质研究

研究了西米淀粉的组成、颗粒形貌及糊化、透明度、老化方面的性质,并与木薯和马铃薯进行了比较。结果表明,西米淀粉的蛋白质含量为0.21%,直链淀粉含量为28%,颗粒为椭圆形,西米淀粉的起糊温度为70.3℃,热糊稳定性高,凝沉性比薯类淀粉弱,西米淀粉的透明度为57.5%,比薯类淀粉易老化。为进一步了解西米淀粉的特性及应用开发提供了一定的理论依据。     

Quantification of trace elements in raw cow’s milk by inductively coupled plasma mass spectrometry (ICP-MS)

The levels of trace elements are an important component of safety and quality of milk. While certain elements such as chromium are essential at low levels, an excess can result in deleterious effects on human health. International quality control standards for milk are published by the Codex Alimentarious Commission and levels of heavy metals in milk intended for human consumption are routinely monitored. This paper describes a new method for demonstrating the levels of V, Cr, Mn, Sr, Cd and Pb in raw cow’s milk, using an ICP-MS. Samples (n = 24) of raw cow’s milk were collected from dairy farms close to mines in Gauteng and North West Provinces of South Africa. In order to destroy organic matrix, each freeze dried milk sample was mineralised by using a microwave assisted digestion procedure. Concentrations of trace elements in digested milk samples were measured by ICP-MS. A whole milk powder reference material (NIST SRM 8435) was used to evaluate the accuracy of the proposed method. It was found that the levels of V, Cr, Mn, Sr, Cd and Pb obtained using the new method showed concordance with certified values.     

Effects of salt and ammonium hydroxide on the quality of ground buffalo meat

The objective of this study was to evaluate the effects of ammonium hydroxide (AH) and sodium chloride on the quality of ground buffalo meat patties. Ground buffalo meat was treated with distilled water (control), 0.5% v/w AH, 1.0% v/w AH, 2.0% v/w AH and 1.0% w/w sodium chloride was added for all the samples. Treatment with AH increased (P<0.05) the pH and water holding capacity (WHC) of ground buffalo meat patties during storage relative to their controls. Hunterlab a* (redness) and chroma values increased (P<0.05) and hue decreased (P<0.05) in all AH treated samples in comparison to controls during storage. Ammonium hydroxide significantly (P<0.05) inhibited metmyoglobin formation compared to control after 3rd day of storage. There was a significant (P<0.05) reduction in thiobarbituric acid reactive substances (TBARS) values in all AH treated samples compared to control throughout storage. These results indicate the potential antioxidant and myoglobin redox stabilizing effect of AH in ground buffalo meat patties.     

Effect of precooking time and drying temperature on the physico-chemical characteristics and in-vitro carbohydrate digestibility of taro flour

Achu is a thick porridge obtained by cooking and pounding taro (Colocasia esculenta) corms and cormels in a mortar. This study was undertaken with the objective of producing precooked taro flour that can be used in the preparation of achu. Taro slices were precooked to times of 0, 20, 45 and 90 min and dried in an air convection oven at varying temperatures of 50, 60, 70 or 80 °C before milling into flour which was then analysed for its water absorption capacity (WAC), water solubility index, emulsion activity and stability, bulk density, foam capacity and least gelation concentration (LGC). Achu made from the flours were equally analysed for their relative penetrometric index, bulk density and colour. The results showed that precooking induced significant (P<0.05) decrease in foam capacity, penetrometric index, and increase in LGC, emulsion stability and WAC. The drying temperature also induces significant reduction in emulsion capacity and stability, penetrometric index, and increase in LGC, WAC. Long precooking time (>45 min) and drying temperature (>60 °C) induced significant reduction of the in-vitro carbohydrate digestibility of taro achu.     

Effects of standardization of whole milk with dry milk protein concentrate on the yield and ripening of reduced-fat cheddar cheese

Commercial milk protein concentrate (MPC) was used to standardize whole milk for reduced-fat Cheddar cheesemaking. Four replicate cheesemaking trials of three treatments (control, MPC1, and MPC2) were conducted. The control cheese (CC) was made from standardized milk (casein-to-fat ratio, C/F approximately 1.7) obtained by mixing skim milk and whole milk (WM); MPC1 and MPC2 cheeses were made from standardized milk (C/F approximately 1.8) obtained from mixing WM and MPC, except that commercial mesophilic starter was added at the rate of 1% to the CC and MPC1 and 2% to MPC2 vats. The addition of MPC doubled cheese yields and had insignificant effects on fat recoveries (approximately 94% in MPC1 and MPC2 vs. approximately 92% in CC) but increased significantly total solids recoveries (approximately 63% in CC vs. 63% in MPC1 and MPC2). Although minor differences were noted in the gross composition of the cheeses, both MPC1 and MPC2 cheeses had lower lactose contents (0.25 or 0.32%, respectively) than in CC (0.60%) 7 d post manufacture. Cheeses from all three treatments had approximately 10(9) cfu/g initial starter bacteria count. The nonstarter lactic acid bacteria (NSLAB) grew slowly in MPC1 and MPC2 cheeses during ripening compared to CC, and at the end of 6 mo of ripening, numbers of NSLAB in the CC were 1 to 2 log cycles higher than in MPC1 and MPC2 cheeses. Primary proteolysis, as noted by water-soluble N contents, was markedly slower in MPC1 and MPC2 cheeses compared to CC. The concentrations of total free amino acids were in decreasing order CC > MPC2 > MPC1 cheeses, suggesting slower secondary proteolysis in the MPC cheeses than in CC. Sensory analysis showed that MPC cheeses had lower brothy and bitter scores than CC. Increasing the amount of starter bacteria improved maturity in MPC cheese.