不同热处理对酸奶品质特性的影响

试验选取经过不同热处理后的鲜奶,分别制成不同的搅拌型和凝固型酸奶,以未变性乳清蛋白含量、黏度、乳清析出率、pH、色泽和感官评价等为指标,研究不同热处理条件对该条件下制得的搅拌型和凝固型酸奶相关指标的影响及其贮藏期间品质的变化。结果表明,当加热条件为95℃、10 min处理原料,即未变性乳清蛋白含量为0.631 mg/m L时,酸奶的感官评价、色泽比较好,在储藏期间的黏度较高、乳清析出率低,在储藏期间能保持较好的稳定性和品质特征。     

添加复原乳对酸奶品质的影响

为探究添加复原乳对酸奶品质的影响,以含有不同比例（0%、20%、40%、60%、80%和100%）复原乳的原料发酵酸奶,以感官评分、酸度、粒径、质构、乳清析出率和糠氨酸含量为指标评价酸奶品质。结果表明：随着复原乳比例的增加,酸奶的感官评分逐渐降低,酸度变化幅度增大,硬度增大,而黏着性降低,乳清析出率增大,持水性变差。与以生鲜乳为原料制作的酸奶相比,含复原乳的原料发酵酵所得的酸奶颗粒粒径较大,且糠氨酸含量升高,品质变差。     

杀菌方式对卤制风味四角蛤蜊产品贮藏品质的影响

目的 为探究不同杀菌方式对四角蛤蜊卤制风味产品在贮藏期间品质的影响。方法对四角蛤蜊卤制风味产品分别进行超高压杀菌、巴氏杀菌和高温杀菌，并在4 ℃下进行贮藏，对其菌落总数、质构、色差、pH值、硫代巴比妥酸（thiobarbituric acid，TBA)值、感官指标、电子鼻、电子舌和挥发性风味物质进行测定。结果 巴氏杀菌和高温杀菌能够较好的抑制微生物的繁殖，分别在贮藏第30 d和第60 d时菌落总数均低于国家标准。随着贮藏时间的延长，各组的TBA值都逐渐升高，感官评分逐渐降低。超高压杀菌在贮藏第15 d时超过国家限制标准，但对产品的质构和色差影响效小。不同杀菌方式均会对产品的风味产生一定的影响，但超高压杀菌对其影响最小。结论 超高压杀菌能够较好的保护产品的质构、色泽和风味，但货架期较短。巴氏杀菌和高温杀菌可以较好的延长产品的货架期，但对产品的质构、色泽和风味破坏较大。     

乳清浓缩蛋白对搅拌型酸奶品质特性影响的研究

研究了以全脂奶粉和乳清浓缩蛋白（WPC-3503）为原料，按照全脂奶粉：乳清浓缩蛋白为100：0，90：10，80：20，70：30的质量配比生产乳固形物含量为12％的酸奶，对含有不同乳清蛋白比例的酸奶在贮藏过程中理化特性、乳酸菌总数的变化以及感官特性进行了比较分析。结果表明，WPC-3503代替10％-20％全脂奶粉生产酸奶时，在贮藏过程中可减缓pH值及酸度的变化速度，提高酸奶的黏度和保水率，改善感官特性，但对乳酸菌总数无明显的影响。     

乳清分离蛋白与燕麦β-葡聚糖作为增稠剂在酸奶中的应用

将乳清分离蛋白(WPI)与燕麦β-葡聚糖(β-G)以不同比例混合,热处理后添加到酸奶中,研究乳清分离蛋白/燕麦β-葡聚糖热复合物对酸奶理化、质构及感官特性的影响。分别与单独添加WPI、聚合乳清蛋白(PWP)及β-葡聚糖的酸奶样品比较,考察了酸奶的pH值、总可溶性固形物、蛋白和脂肪质量分数、质构、黏度、持水力和感官特性等指标。结果表明,WPI/β-G比例为30∶1,pH值为7.0,85℃条件下加热30 min时得到的复合物,以质量分数为2%的添加量制备酸奶,其黏度、硬度、持水力较高,感官评价较好。综合研究发现,WPI/β-G复合物可有效改善酸奶的凝胶特性及相关的理化指标,增加了酸奶的口感、风味及组织状态,提高了酸奶的品质。     

马乳酒样乳杆菌ZW3对酸奶风味及质构的影响

将马乳酒样乳杆菌马乳酒样亚种ZW3（Lactobacillus kefiranofaciens subsp. kefiranofaciens ZW3）与常用的酸奶发酵剂嗜热链球菌和保加利亚乳杆菌共同发酵,旨在制备酸奶时,不添加任何增稠剂和乳化剂,而是通过乳酸菌的发酵作用,增加酸奶的黏度和适口性。结果表明,ZW3可以缩短酸奶发酵时间,提高持水力,减少乳清析出,增加黏度,改善流变学特性,增加酸奶的硬度、胶着性、咀嚼性、内聚性和恢复性,电子鼻分析及感官评价结果表明,ZW3可提高酸奶中挥发性风味物质的含量,改善酸奶风味及口感。     

搅拌型酸奶在不同贮藏条件下品质变化的研究

选用同一批次的搅拌型酸奶分别在6℃、20℃、30℃三种不同温度条件下进行贮藏,每隔2d测定酸奶的感官、理化和微生物指标,从而确定搅拌型酸奶在不同贮藏条件下的品质变化。在贮藏过程中,由于温度的变化,会导致酸奶品质发生一些列的变化。比如,酸味太重,乳清析出,产品有不良风味等。     

肉桂多糖对乳酸菌发酵及酸奶品质的影响

以肉桂多糖为研究对象,通过测定pH、乳酸菌菌落数、乳清的析出率、黏度、保水性、滴定酸度以及感官评定等指标,从而进行研究肉桂多糖对乳酸菌发酵及酸奶在常温贮藏与冷藏贮藏过程中的品质变化影响。研究结果表明:通过加入0, 0.5%, 1.0%, 1.5%, 2.0%的肉桂多糖进行研究,肉桂多糖的添加量在1.0%时,感官评分最高,达90.8,乳清的析出率最低,肉桂多糖既可以稳定维持酸奶酸度变化,又能促进乳酸菌变化,黏度比空白对照组高,酸奶的保水性得到了提高。在冷藏与常温条件下对比,冷藏比常温条件下的酸奶乳清的析出率少、酸度稳定、黏度大、保水性好,添加适量的肉桂多糖在一定程度上可以延长酸奶保质期,同时冷藏保存也有利于提高酸奶的品质。     

贮藏条件对红薯叶酸菜品质的影响

目的:探寻乳酸菌发酵红薯叶酸菜的贮藏条件及贮藏期间品质变化规律。方法:真空包装后以常温25℃、低温4℃、80℃—15 min巴氏杀菌后4℃、85℃-10 min巴氏杀菌后4℃贮藏,比较4个条件下红薯叶酸菜pH值、乳酸含量、亚硝酸盐含量、菌落数、色差值及感官评分。结果:25℃下贮藏亮度下降最快,第60天色泽明显变深;4℃下贮藏第30天的酵母菌数量最多,第45天的乳酸菌数量最多;80℃-15 min杀菌后贮藏第90天的大肠杆菌数量最少,感官评分达到食用临界值;85℃-10 min杀菌后贮藏第75天的总菌数量最少,感官评分及格。pH值与亚硝酸盐含量呈极显著负相关,与L值、感官评分呈极显著正相关;乳酸菌数与酵母菌、大肠杆菌、总菌数呈极显著正相关,其中感官评分在第一主成分中的载荷量最大。结论:80℃-15 min杀菌后4℃贮藏,其主要微生物为乳酸菌,其他指标均符合安全标准,感官品质稳定,更适合作为酸菜的贮藏条件,贮藏期可达90 d。     

大豆蛋白酶解产物对不同发酵剂酸奶品质的影响

本文研究了大豆蛋白酶解产物(Soy protein hydrolysate,SPH)对187、495和885三种发酵剂酸奶发酵过程中p H值变化和贮藏过程中乳清析出、流变特性和质构特性的影响。结果表明,SPH对3种酸奶均具有一定的促发酵效果,其中对以187和495为发酵剂的p H值下降速度较慢的酸奶促发酵效果更明显。贮藏过程中,SPH可有效减缓酸奶乳清析出,其中对以885为发酵剂的乳清析出率最高的酸奶作用最明显,降低率达到49.35%。此外,SPH可有效提高187和495发酵剂酸奶的表观黏度和触变环面积,有利于酸奶结构的恢复。通过对酸奶第7 d流变和质构特性的进一步研究,SPH可显著提高3种酸奶的稠度和零剪切黏度,降低其流动指数、柔量和粘性指数,从而有效改善3种酸奶的流变和质构特性,提高酸奶在低应力下稳定性,降低其在高应力下形变破坏程度。     

Application of whey protein emulsion gel microparticles as fat replacers in low-fat yogurt: Applicability of vegetable oil as the oil phase

Low-fat, healthy yogurt is becoming increasingly favored by consumers. In the present study, whey protein emulsion gel microparticles were used to improve the quality of low-fat yogurt, and the effects of vegetable oil emulsion gel as a fat substitute on the qualities of low-fat yogurt were investigated, expecting to obtain healthier and even more excellent quality low-fat yogurt by applying a new method. First, emulsion gel microparticles were prepared, and then particle size distribution of emulsion gel and water holding capacity (WHC), textural properties, rheological properties, microstructure, storage stability, and sensory evaluation of yogurt were carried out. The results showed that yogurt with emulsion gel had significantly superior qualities than yogurt made with skim milk powder, with better WHC, textural properties, rheological properties, and storage stability. The average particle size of whey protein-vegetable oil emulsion gel microparticles was significantly larger than that of whey protein-milk fat emulsion gel microparticles, and the larger particle size affected the structural stability of yogurt. The WHC of yogurt made with whey protein-vegetable oil emulsion gel microparticles (V-EY) was lower (40.41%) than that of yogurt made with whey protein-milk fat emulsion gel microparticles (M-EY; 42.81%), and the texture results also showed that the hardness, consistency, and viscosity index of V-EY were inferior to these of M-EY, whereas no significant differences were found in the cohesiveness. Interestingly, the microstructure of V-EY was relatively flatter, with more and finer network branching. The whey separation between V-EY and M-EY also did not show significant differences during the 14 d of storage. Compared with yogurt made with whey protein, vegetable oil, and skim milk powder, the structure of V-EY remained relatively stable and had no cracks after 14 d of storage. The sensory evaluation results found that the total score of V-EY (62) was only lower than M-EY (65) and significantly higher than that of yogurt made with skim milk powder. The emulsion gel addition improved the sensory qualities of yogurt. Whey protein emulsion gel microparticles prepared from vegetable oil can be applied to low-fat yogurt to replace fat and improve texture and sensory defects associated with fat reduction.     

热处理和转谷氨酰胺酶对凝固型酸乳品质的影响

为了揭示热处理和转谷氨酰胺酶(Transglutaminase,TGase)共同作用对凝固型酸乳品质的影响,本研究以不同条件热处理(70℃ 15 min、80℃ 15 min、90℃ 15 min、95℃ 5 min)的牛乳为原料,在发酵的同时添加不同浓度(0、5、10 U)TG酶,制得凝固型酸乳,并对其总体颜色变化值(ΔE)、持水性、硬度、pH和感官评分进行测定。结果表明,热处理温度由70℃升高到95℃会使酸乳(0 U,TGase)的ΔE升高18.86%,持水率升高12.39%,硬度升高7.48%,储存24 h和21 d时的pH分别降低0.19和0.13,并获得更浓郁的乳香。TG酶处理可以改善酸乳的稠度、口感、组织结构等感官特性,明显提高酸乳的持水率,降低色差和减缓后酸化速率,其作用效果随着TG酶浓度的升高而增大。在95℃下热处理5 min,添加10 U TG酶的酸乳拥有更好的品质特性,其色差较相同温度未加入TG酶的酸乳降低8.11%,持水率升高5.56%,储存24 h和21 d时的pH分别降低0.08和0.38,硬度也提升了23.30%。研究表明热处理和TG酶对提高酸乳的品质并改善酸乳的凝胶结构起协同作用,95℃热处理5 min,加入10 U TG酶可能是生产凝固型酸乳的最佳条件。     

冷藏即食虾仁保藏期间品质变化

目的:制备一种高水分虾仁即食调理食品(水分含量>70%,水分活度>0.95),并对其冷藏保藏期间品质变化进行了研究。方法:活虾去虾头、壳及肠线后,100 ℃ 沸水浴预煮2 min,沥干水后进行真空包装,然后进行二次沸水浴100 ℃热处理10 min,最后微波(600 W)处理2 min。研究冷藏即食虾仁在保藏期间(4 ℃,7 d)水分含量、水分活度、残余内源酶活力、质构、风味物质、微生物等指标的变化。结果:产品在保藏期内水分含量和水分活度没有显著变化;质构方面,产品的回复性略有降低、粘性略有升高,弹性及硬度等没有显著性变化;残余内源酶活力在保藏期间变化幅度不超过1%;虽醇类、酯类和烷烃类等风味物质略有增加,但整体感官品质仍然可以接受,产品的微生物总数低于104 CFU/g,且重金属含量均低于0.5 mg/kg。采用水煮、真空包装、微波处理、低温保藏相结合制备的虾仁即食调理食品,在预设货架期7 d内可以保持较高的水分活度和良好的感官品质。     

发酵温度波动对酸奶感官、质构和风味特性的影响

为研究发酵温度波动对酸奶品质的影响,本实验测定了酸奶凝乳时间、酸度、pH和质构指标,用模糊数学法分析了感官指标,并用气相色谱-质谱联用仪(GC-MS)测定了酸奶风味成分,探讨了4种温度波动对酸奶发酵特性和品质的影响。结果表明,与对照组相比,处理组1(41 ℃-42 ℃-43 ℃)酸奶的凝乳时间、质构和感官指标无显著差异(p>0.05);处理组2(36 ℃-38 ℃-42 ℃)凝乳时间增加(p<0.05),硬度、内聚性及感官无显著差异(p>0.05),胶黏性减小(p<0.05);处理组3(42 ℃-38 ℃-36 ℃)凝乳时间、内聚性无显著差异(p>0.05),硬度和胶黏性降低(p<0.05),感官评分显著增加(p<0.05);处理组4(42 ℃-46 ℃-48 ℃)和处理组5(48 ℃-46 ℃-42 ℃)凝乳时间、内聚性及感官无显著差异(p>0.05),硬度显著增大(p<0.05),胶黏性显著减小(p<0.05)。所有处理间的酸度及pH无显著差异(p>0.05)。不同的温度波动处理组间主要挥发性风味物质种类基本相同,但含量存在差异。在实际生产中,对酸奶发酵温度的控制可以不必非常精确,允许小范围波动。     

Lutein Is Stable in Strawberry Yogurt and Does Not Affect its Characteristics

ABSTRACT:  The impact of various levels of lutein on the physicochemical, microbiological, and sensory characteristics of yogurt over its shelf life was determined. Nonfat strawberry yogurts were prepared with 0, 0.5, 1.5, and 3.0 mg lutein per 170 g serving (20% overages were included to account for processing losses). The lutein was incorporated prior to homogenization of the yogurt mix. Stability of lutein, viscosity, pH, syneresis, standard plate counts, coliform counts, color (L*, a*, b*), and sensory evaluation (flavor, body and texture, and appearance and color) were measured at weeks 0, 1, 3, and 5 after product manufacture. The interaction effect between levels of lutein and storage time was significant for a* (redness-greenness) values. Lutein levels remained above target throughout the 5-wk storage study. Lutein did not affect viscosity, pH, syneresis, L* (lightness) and b* (yellowness-blueness) values, standard plate counts, coliform counts, flavor, body, texture, appearance, and color scores. These results suggested that lutein was suitable for inclusion in functional yogurts. The skin and eye health benefits provided by lutein can easily be incorporated into yogurt to complement inherent nutritional properties.     

Use of acid whey protein concentrate as an ingredient in nonfat cup set-style yogurt

Acid whey resulting from the production of soft cheeses is a disposal problem for the dairy industry. Few uses have been found for acid whey because of its high ash content, low pH, and high organic acid content. The objective of this study was to explore the potential of recovery of whey protein from cottage cheese acid whey for use in yogurt. Cottage cheese acid whey and Cheddar cheese whey were produced from standard cottage cheese and Cheddar cheese-making procedures, respectively. The whey was separated and pasteurized by high temperature, short time pasteurization and stored at 4°C. Food-grade ammonium hydroxide was used to neutralize the acid whey to a pH of 6.4. The whey was heated to 50°C and concentrated using ultrafiltration and diafiltration with 11 polyethersulfone cartridge membrane filters (10,000-kDa cutoff) to 25% total solids and 80% protein. Skim milk was concentrated to 6% total protein. Nonfat, unflavored set-style yogurts (6.0 ± 0.1% protein, 15 ± 1.0% solids) were made from skim milk with added acid whey protein concentrate, skim milk with added sweet whey protein concentrate, or skim milk concentrate. Yogurt mixes were standardized to lactose and fat of 6.50% and 0.10%, respectively. Yogurt was fermented at 43°C to pH 4.6 and stored at 4°C. The experiment was replicated in triplicate. Titratable acidity, pH, whey separation, color, and gel strength were measured weekly in yogurts through 8 wk. Trained panel profiling was conducted on 0, 14, 28, and 56 d. Fat-free yogurts produced with added neutralized fresh liquid acid whey protein concentrate had flavor attributes similar those with added fresh liquid sweet whey protein but had lower gel strength attributes, which translated to differences in trained panel texture attributes and lower consumer liking scores for fat-free yogurt made with added acid whey protein ingredient. Difference in pH was the main contributor to texture differences, as higher pH in acid whey protein yogurts changed gel structure formation and water-holding capacity of the yogurt gel. In a second part of the study, the yogurt mix was reformulated to address texture differences. The reformulated yogurt mix at 2% milkfat and using a lower level of sweet and acid whey ingredient performed at parity with control yogurts in consumer sensory trials. Fresh liquid acid whey protein concentrates from cottage cheese manufacture can be used as a liquid protein ingredient source for manufacture of yogurt in the same factory.     

Industrial yogurt manufacture: monitoring of fermentation process and improvement of final product quality

Lactic acid fermentation during the production of skim milk and whole fat set-style yogurt was continuously monitored by measuring pH. The modified Gompertz model was successfully applied to describe the pH decline and viscosity development during the fermentation process. The viscosity and incubation time data were also fitted to linear models against ln(pH). The investigation of the yogurt quality improvement practices included 2 different heat treatments (80°C for 30 min and 95°C for 10 min), 3 milk protein fortifying agents (skim milk powder, whey powder, and milk protein concentrate) added at 2.0%, and 4 hydrocolloids (κ-carrageenan, xanthan, guar gum, and pectin) added at 0.01% to whole fat and skim yogurts. Heat treatment significantly affected viscosity and acetaldehyde development without influencing incubation time and acidity. The addition of whey powder shortened the incubation time but had a detrimental effect on consistency, firmness, and overall acceptance of yogurts. On the other hand, addition of skim milk powder improved the textural quality and decreased the vulnerability of yogurts to syneresis. Anionic stabilizers (κ-carrageenan and pectin) had a poor effect on the texture and palatability of yogurts. However, neutral gums (xanthan and guar gum) improved texture and prevented the wheying-off defect. Skim milk yogurts exhibited longer incubation times and higher viscosities, whereas they were rated higher during sensory evaluation than whole fat yogurts.     

西藏牧区自然发酵牦牛酸奶的乳酸菌菌种筛选及工艺优化

采用从西藏、川西青藏高原牧区自然发酵牦牛酸奶中筛选出的发酵性能优良的4 株乳酸菌（LP1、LP2、LP3、LP4）进行组合发酵试验,经过纸片法筛选出优势发酵组合,以及其发酵牦牛酸奶的凝乳时间、滴定酸度、感官评价可以得出（LP1和LP2）组合为本试验的最佳发酵菌种组合。因此选用此菌种组合发酵牦牛酸奶,经过L16（44）正交试验得出牦牛酸奶发酵的最佳工艺条件为：发酵温度42 ℃、接种量6%、加糖量4 g/100 mL、菌种LP1与LP2浓度比为2∶1,此条件下发酵的牦牛酸奶凝固均匀,组织结构光滑细腻,无乳清析出,具有浓郁的酸奶风味。     

Determination of shelf life of concentrated yogurt (labneh) produced by in-bag straining of set yogurt using hazard analysis

Strained yogurt, labneh, produced by straining cow's milk set yogurt in cloth bags, was stored at 5, 15, and 25 degrees C, and changes in microbial counts, pH, titratable acidity, percentage of free whey, and sensory attributes were monitored during storage. Counts of total aerobes, psychrotrophic yeasts, yeasts and molds, and lactic acid bacteria, except in samples stored at 25 degrees C, increased irrespective of storage temperature. The pH of samples decreased, titratable acidity and percentage of free whey increased, and texture defects were detected at a later stage than flavor changes during storage. Shelf-life data of labneh was adequately described by the Weibull distribution. The nominal shelf life determined using sensory changes and yeast counts as failure criteria ranged from 8.5 to 10.5, 4.7 to 5.8 and 2.3 to 2.7 d at 5, 15 and 25 degrees C, respectively. Q10 (shelf life at T degrees C/shelf life at T+10 degrees C) for flavor quality loss was 1.98 at 5 degrees C, and the corresponding activation energy was 11.3 kcal/mol.