Low-fat set yogurt made from milk subjected to combinations of high hydrostatic pressure and thermal processing

The combined use of high hydrostatic pressure (300 to 676 MPa, 5 min) and thermal treatment (85 degrees C, 30 min) in milk for the manufacture of low-fat yogurt was studied. The objective was to reduce syneresis and improve the rheological properties of yogurt, reducing the need for thickeners and stabilizers. The use of high hydrostatic pressure alone, or after thermal treatment, reduced the lightness and increased the viscosity of skim milk. However, milk recovered its initial lightness and viscosity when thermal treatment was applied after high hydrostatic pressure. The MALDI-TOF spectra of skim milk presented monomers of whey proteins after a treatment of 676 MPa for 5 min. Yogurts made from skim milk subjected to 400 to 500 MPa and thermal treatment showed increased yield stress, resistance to normal penetration, and elastic modulus, while having reduced syneresis when compared to yogurts from thermally treated or raw milks. The combined use of thermal treatment and high hydrostatic pressure assures extensive whey protein denaturation and casein micelle disruption, respectively. Although reaggregation of casein submicelles occurs during fermentation, the net effect of the combined HHP and thermal treatment is the improvement of yogurt yield stress and reduction of syneresis.     

High hydrostatic pressure modification of whey protein concentrate for use in low-fat whipping cream improves foaming properties

Whey is the inevitable by-product of cheese production. Whey can be incorporated into a variety of foods, but little has been done to investigate its suitability in whipping cream. The objective of this work was to evaluate the foaming properties of selected low-fat whipping cream formulations containing whey protein concentrate (WPC) that did or did not undergo high hydrostatic pressure (HHP) treatment. Fresh whey was concentrated by ultrafiltration, pasteurized, and standardized to 8.23% total solids and treated with HHP at 300 MPa for 15 min. Viscosity, overrun, and foam stability were determined to assess foaming properties. Sensory evaluation was conducted with 57 panelists using a duo-trio difference test. The optimal whipping time for the selected formulations was 3 min. Whipping cream containing untreated WPC and HHP-treated WPC resulted in greater overrun and foam stability than the control whipping cream without WPC. Panelists distinguished a difference between whipping cream containing untreated WPC and whipping cream containing HHP-treated WPC. High hydrostatic pressure-treated WPC can improve the foaming properties of low-fat whipping cream, which may justify expansion of the use of whey in whipping cream and application of HHP technology in the dairy industry.     

螺旋藻益生菌酸乳的研制

探讨了在纯鲜牛乳中添加螺旋藻制剂,经益生乳酸菌发酵,制得一种浅绿色、风味独特的新型营养保健酸奶.通过四因素三水平L9(34)正交试验确定了最佳配方工艺为:合格鲜牛乳,白砂糖7.0%,果胶0.08%(均为质量分数),益生菌L.casei Zhang 4×106g-1,直投式发酵剂CHR HANSEN YC-X11 0.006%,螺旋藻提取液6.0%,发酵温度42℃,发酵时间4 h.     

Food processing by high hydrostatic pressure

The use of high hydrostatic pressures (HHP) for food processing is finding increased application within the food industry. One of the advantages of this technology is that because it does not use heat, sensory, and nutritional attributes of the product remain virtually unaffected, thus yielding products with better quality than those processed traditional methods. HHP have the ability to inactivate microorganisms as well as enzymes responsible for shortening the life of a product. In addition to lengthening the shelf-life of food products, HHP can modify functional properties of components such as proteins, which in turn can lead to the development of new products. Equipment for large-scale production of HHP processed products are commercially available nowadays. Guacamole, sliced ham, oysters, and fruit juices are some of the products currently available on the market. HHP technology is one of the most promising nonthermal processes.     

High hydrostatic pressure effects on bacterial bioluminescence

The mechanism that leads to microbial inactivation by high hydrostatic pressure remains elusive. In this study, a high-pressure system interfaced with a photomultiplier tube (PMT) was developed to monitor cellular metabolism in situ using bioluminescent bacterial strains. Preliminary characterization of the system was performed using Pseudomonas fluorescens 5RL expressing lux proteins from Vibrio fischeri. Stepwise increases in pressure at 34 MPa and above resulted in decreased bioluminescence. Square wave exposure to pressures of 69, 103 and 138 MPa showed bioluminescence reductions greater than 95%, but when cells were returned to ambient pressure bioluminescence returned to 51, 38, and 4% of initial bioluminescence values, respectively. An Escherichia coli strain expressing lux proteins from V. fischeri was constructed to determine whether this reversible effect could be observed in another bacterial genus. Square wave perturbations of 69, 103 and 138 MPa resulted in bioluminescence reductions of about 94% at the highest pressure treatment. Upon decompression, bioluminescence returned to 74, 58 and 30% of the initial bioluminescence values for cells treated at 69, 103 and 138 MPa, respectively. These results suggest that square wave exposure to pressure up to 138 MPa induces reversible cell damage in P. fluorescens 5RL and E. coli VF lux.     

High hydrostatic pressure processing reduces Salmonella enterica serovars in diced and whole tomatoes

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. One effective post harvest treatment to reduce Salmonella enterica in tomatoes may be high pressure processing (HPP). The objectives of the study were to determine the potential for HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant of the four serovars from fresh diced and whole tomatoes. To evaluate pressure resistance, TSB containing 8 log CFU/ml of one of the four serovars was packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450 or 550 MPa) for 120 s. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150 g) and whole red round tomatoes (approximately 150 g) were inoculated with 0.1 ml of 9.1 log CFU/ml S. Braenderup, and subjected to the same pressure treatments (350, 450 or 550 MPa). Significant reductions of S. Braenderup concentrations in diced tomatoes (P < 0.05) were seen after processing at 350 (0.46 CFU/g), 450 (1.44 log CFU/g), and 550 MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P < 0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550 MPa (3.35 log CFU/g). HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in whole and diced tomatoes.     

低脂菊苣膳食纤维凝固型酸奶的生产工艺

以菊苣膳食纤维和脱脂乳粉为原料,通过乳酸菌发酵生产一种低脂凝固型酸奶。通过单因素试验和均匀设计试验,初步确定最佳发酵工艺条件为:菊苣膳食纤维2.08%,脱脂乳粉12.7%,蔗糖7.06%,发酵剂接种量为0.8 g/L,发酵温度为42.8℃,发酵时间为7.5 h。     

柚子酸奶的研究

以柚子汁和脱脂奶粉为主要原料,研究柚子酸奶的生产工艺.实验确定了袖子汁添加量10%、白砂糖9%、接种量7%,发酵时间4.5h、杀茵温度90℃、杀菌时间10min;复合稳定剂种类与配比为:黄原胶0.03%、羧甲基纤维素钠(CMC-Na)0.08%、卡拉胶0.005%.产品具有柚子和酸乳所特有的香气,爽滑细腻,既营养又保健,有着广阔的市场前景.     

Effect of calcium on the physical properties of stirred probiotic yogurt

The effect of calcium on the viscosity, firmness, and smoothness, as determined by extent of nodulation, of stirred probiotic yogurt produced by bacterial fermentation was investigated. Standardized milk for yogurt manufacture was prepared, and calcium was added or removed from the system. Calcium was added as Ca²⁺ in the form of CaCl₂ (up to 13.6 mM) or nonionic calcium as Gadocal-K (calcium potassium citrate; up to 49.8 mM). Calcium was removed by chelating with sodium citrate (up to 16 mM) or by cation exchange with Amberlite IR-120 plus (sodium form) resin (up to 10 g/L). Calcium chloride and sodium citrate were added either before or after heat treatment of milk, and nonionic calcium was added before heat treatment. Calcium removal by ion exchange was performed before heat treatment. Neither Ca²⁺ addition nor removal by chelation with citrate resulted in stirred yogurt with viscosity, firmness, and smoothness superior to those of the control yogurt, whereas addition of 49.8 mM nonionic calcium and removal of calcium (5.6 mM or ∼10% of total calcium) by cation exchange improved the firmness and viscosity without affecting yogurt smoothness. The study identified Gadocal-K as a possible source of calcium fortification of stirred yogurt without loss of texture.     

High hydrostatic pressure/temperature modeling of frankfurter batters

The impact of high pressure/temperature treatment on structure modification and functional sensory properties of frankfurter batter was investigated. The degree of solubilization of meat proteins, particularly of myosin, was identified as a key process with significant effect on the batter's structural properties. The maximal solubilization level was at 200 MPa/40 °C IT for all formulations which was found to be treatment time dependent. The impact of the pressurizing gradient — PG = 40 MPa/s and PG = 2.5 MPa/s was investigated and estimated to have a significant effect on the protein network and functional properties, respectively. These were improved at low PG (2.5 MPa/s) as a phenomenon of secondary network formation parallel to the main matrix. Batter secondary-structure characteristics were found to be ionic-strength dependent. According to SDS-PAGE analysis, the major role in the solubilization, aggregation and gelation processes occurring in the aqueous phase was due to the myosin S-1 and S-2, N-terminal, C-terminals, the MLC and actin during the high pressure/temperature treatment.     

灵芝多糖益生菌酸奶抗衰老的研究

对D-半乳糖致衰老小鼠分别灌胃添加不同含量灵芝多糖的益生菌酸奶,测定各组处理小鼠脏器指数,血清及不同组织中超氧化物歧化酶(SOD)、丙二醛(MDA)、谷胱甘肽过氧化物酶(GSH-PX)、过氧化氢酶(CAT)活性指标,研究添加灵芝多糖的益生菌酸奶对D-半乳糖致衰老小鼠抗衰老作用的效果。结果表明:添加灵芝多糖的益生菌酸奶可显著提高衰老模型小鼠血清及不同组织中SOD、CAT、GSH-PX活性、降低MDA含量(P0.05),且以高剂量组[1 200 mg/(kg·d)]效果最优。与衰老模型组相比,高剂量组[1 200 mg/(kg·d)]小鼠血清、肝脏、脑组织中SOD活力依次提高20.34%、8.39%、48.95%;小鼠血清、肝脏中GSH-PX活力依次提高38.45%、39.67%;小鼠血清、肝脏、脑组织中MDA含量分别降低38.37%、43.97%、38.39%;小鼠脑组织、肝脏、肾脏中CAT活力依次提高60.02%、55.29%、37.73%。与酸奶组相比,高剂量组小鼠SOD活力依次提高18.36%、1.58%、25.13%;GSH-PX活力依次提高38.45%、30.26%;MDA含量分别降低10.47%、30.96%、18.91%;CAT活力依次提高41.31%、32.07%、26.64%。结论:灵芝多糖添加入植物乳杆菌益生发酵酸奶可发挥灵芝多糖和益生菌酸奶在抗衰老功能方面的协同作用发挥更强抗衰老效果。     

凝胶型酸奶加工工艺研究

提出了一种新型酸奶制品———凝胶型酸奶的加工工艺和技术条件,并就发酵终点酸度和氯化钙添加量对产品凝胶性的影响进行了试验分析,确定了最佳工艺参数。     

嗜酸乳杆菌发酵乳的研究

以嗜酸乳杆菌和嗜热链球菌为发酵剂,发酵制成具有保健功能的新型酸乳——嗜酸乳杆菌发酵乳。     

超高压对冷藏带鱼段的保鲜效果

研究了超高压预处理对4℃冷藏带鱼段保鲜效果的影响。试验以4℃冷藏带鱼段做对照,设置不同压力和保压时间(220 MPa、290 MPa,3、6、9 min)对带鱼进行超高压预处理后4℃贮藏,共7个试验组,每隔1天测定感官评定、菌落总数(TPC)、持水力(WHC)、挥发性盐基氮(TVB-N)、三甲胺氮(TMA-N)和硫代巴比妥酸(TBA)等指标。结果表明:超高压能有效抑制菌落的增殖,压力越高,保压时间越长,抑制作用越明显。冷藏组带鱼的货架期为4 d,220 MPa组的货架期延长至10 d,290 MPa组的货架期延长至12 d。随着压力的增大、保压时间的延长,超高压处理后鱼肉的透明度减少,持水力有所降低,但能有效抑制TMA-N的增长速度,并在一定程度上抑制带鱼的脂肪氧化。新鲜带鱼超高压处理后的TVB-N会随着压力的增大有所增加,在贮藏过程中,冷藏组的TVB-N的增长速度逐渐超过超高压组,且保压时间越长、压力越大,抑制TVB-N作用越好。其中290 MPa、6min超高压处理组,290 MPa、9 min超高压处理组保鲜效果最好,贮藏12 d时,带鱼的细菌总数分别为6.19、6.04 lg(CFU/g),TVB-N分别为19.87、20.86 mg N/100 g,基本都处在带鱼二级鲜度之内。     

High hydrostatic pressure effects on immunoreactivity and nutritional quality of soybean products

The aim of this research was to evaluate the protein pattern, immunoreactivity and amino acid composition of soybean seeds and commercial tofu after treating by high hydrostatic pressure (HHP) (300 MPa, 15 min, 40 °C), as well as of sprouts obtained from unpressurised and HHP-treated seeds. HHP did not affect the electrophoretic profile of soybean seeds or tofu protein extracts, but lower intensity of some protein bands were observed in HHP-treated products. A significant (P ? 0.05) reduced antigenicity was observed in the sprouts from HHP-treated seeds compared to the sprouts from untreated seeds, while higher antigenicity of the pressurised seeds compared with the untreated ones was found. HHP decreased the total essential amino acid content as well as two nutritional indexes, the Chemical Score (CS) and the Essential Amino Acid Index (EAAI), but only by 18%. The findings suggest that HHP applied to soybean seeds before germination could constitute a valuable technological approach for the industrial production of nutritive hypoallergenic soybean sprouts.     

Model for Listeria monocytogenes inactivation on dry-cured ham by high hydrostatic pressure processing

The aim of the work was to develop and validate a model of the inactivation of Listeria monocytogenes on dry-cured ham by high hydrostatic pressure (HHP) processing, as a function of the technological parameters: intensity, length and fluid temperature. Dry-cured ham inoculated with L. monocytogenes was treated at different HHP conditions (at 347-852 MPa; for 2.3 to 15.75 min; at 7.6 to 24.4 °C) following a central composite design. Bacterial inactivation was assessed in terms of logarithmic reductions of L. monocytogenes counts on selective media. According to the best fitting and most significant polynomial equation, pressure and time were the most important factors determining the inactivation extent. The significance of the quadratic term of pressure and time indicated that little effect was observed below 450 MPa, whereas holding time longer than 10 min did not result in a meaningful reduction of L. monocytogenes counts. Temperature did not show significant influence at the range assayed. The model was validated with results obtained from further experiments and bibliographical data within the range of the experimental domain. The accuracy factor and bias factor were within the proposed acceptable values indicating the suitability of the model for predictive purposes, such as prediction of the process criteria to meet the Food Safety Objectives. The results of this work may help food processors to select optimum processing conditions of HHP.     

High hydrostatic pressure treatment of finfish to inactivate Anisakis simplex

High hydrostatic pressure has been demonstrated to be a useful technique for treating food to reduce the number of pathogenic organisms and to extend shelf life. Most research in this area has focused on bacteria. However, a concern in the sashimi (raw fish) industry is that nematode worms such as Anisakis simplex occur naturally in cold-water marine fish. The objectives of this research were to perform a pilot study to determine the effect of high hydrostatic pressure on the viability of Anisakis simplex larvae, commonly found in king salmon and arrowtooth flounder, and to evaluate the effects of high hydrostatic pressure on the color and texture of the fish fillets. Pieces of fish (ca. 100 g per bag) containing 13 to 118 larvae were exposed to pressures of up to 80,000 lb/in2 (552 MPa) for up to 180 s. The times and pressures required to kill 100% of the larvae were as follows: 30 to 60 s at 60,000 lb/in2 (414 MPa), 90 to 180 s at 40,000 lb/in2 (276 MPa), and 180 s at 30,000 lb/in2 (207 MPa). For all salmon treatments that killed 100% of the larvae, a significant increase in the whiteness of the flesh was observed. Although high hydrostatic pressure was effective in killing A. simplex larvae in raw fish fillets, its significant effect on the color and overall appearance of the fillet may limit its application to the processing of fish for raw-fish markets.     

脂肪质量分数对低脂Mozzarella干酪微观结构的影响

使用扫描电子显微镜观察了不同脂肪质量分数低脂Mozzarella干酪成熟0 d及30 d的微观结构.结果表明,以全脂Mozzarella干酪为对照,成熟0 d时,脱脂及部分脱脂Mozzarella干酪蛋白结构致密,中脂Mozzarella干酪网络结构较明显,且有一定数量的孔洞;成熟30 d时,脱脂Mozzarella干酪变化较小,部分脱脂Mozzarella干酪仅光滑度提高,中脂Mozzarella干酪则接近于全脂Mozzarella干酪.     

不同益生菌的加入对酸奶储藏期内风味的影响

以LGG、NCFM、BB-12和ABY四种益生菌酸奶为研究对象,跟踪检测这些样品在20℃储藏条件下的滴定酸度、益生菌活菌数、双乙酰含量和乙醛含量,比较不同益生菌对酸奶风味及酸度的影响。研究表明,在20℃常温储藏条件下,4种益生菌都不同程度地加速了酸奶的后酸化,其中以LGG和NCFM最为明显;除LGG外,NCFM,BB-12和ABY在酸奶储藏期内的存活率都呈下降趋势;不同益生菌酸奶中双乙酰含量和乙醛含量有明显差异,在添加LGG的酸奶中含量最低,在添加NCFM的酸奶中含量最高。