复原乳与生鲜乳发酵差异性分析

<正>复原乳是指把鲜牛奶浓缩、干燥成为浓缩乳或乳粉,再添加适量水,制成与原乳中水、固体物比例相当的液态奶。生鲜乳是一种营养价值仅次于母乳的液体食品,正常情况下呈白色胶体状态。本实验通过测定p H、滴定酸度、乳糖含量和凝乳状态等特异性指标,研究复原乳和鲜牛乳在乳酸菌发酵过程中的差异性。其中,p H和     

源于不同原料乳曲拉的品质分析

为了比较分析牦牛乳、犏牛乳、黑白花牛乳和利用这3种牛乳所制曲拉的品质差异,以3种牛乳及其所制曲拉为研究对象,对3种牛乳的理化性质和3种曲拉在发酵过程中p H、滴定酸度、持水力、感官品质及质构特性进行了测定分析。结果表明:3种牛乳及其所制曲拉的品质之间存在一定差异。其中,牦牛乳的干物质含量为18.30%,蛋白质含量为5.80%、脂肪含量为6.15%,显著高于犏牛乳和黑白花牛乳(p0.05);犏牛乳的乳糖含量最高,其干物质、蛋白质和脂肪含量也较高;犏牛曲拉在发酵过程中的p H、滴定酸度、持水力、感官品质及质构特性与牦牛曲拉非常相近,表明其制作曲拉的品质与牦牛曲拉类似,说明犏牛乳在一定程度上可以替代牦牛乳作为曲拉的原料乳,用以解决牦牛乳资源短缺的难题。     

热处理对水牛乳物化性质的影响

为了探索、比较水牛乳经不同热处理条件处理后,其部分物化性质的变化,对在广西皇氏乳业云表生态奶水牛基地采集的15份杂交高代水牛乳样品,经不同条件热处理后的色泽度、p H值、滴定酸度、p H值缓冲容量及电导率进行了分析比较。结果表明,与未经处理的水牛乳样品相比,水牛乳经不同条件热处理后,其色泽度、p H值、滴定酸度、p H值缓冲容量及电导率皆发生显著变化。其中,在本实验研究范围内,水牛乳在经121℃(15 min)处理后,其滴定酸度、缓冲容量和电导率分别达到最大值21°T,浓度0.0140 mol/L和3.905 ms/cm;在经95℃(5 min)处理后,其p H值缓冲容量与电导率有最小值0.0063 mol/L和3.600 ms/cm。     

乳脂肪含量对牛乳理化性质的影响

以人工制备的不同含脂量（0.5%、1.5%、2.5%、3.5%）的牛乳为样品（不同批次,n=12）,对其成分、显微结构、粒径、色度和稳定性进行对比分析。结果表明,随着含脂量的增加,牛乳中总固形物含量及酪蛋白含量显著增加（P＜0.05）,蛋白质含量差异不显著（P＞0.05）。新鲜牛乳的酸度在16～18 °T范围内,其大小与含脂量高低成正比,另外,含脂量越高,牛乳中脂肪球粒径越大,体系越不稳定,色泽越黄。本实验为探索牛乳脂肪含量和其理化性质之间的关系提供基础数据,为牛乳制品的研发及生产工艺优化提供了技术依据。     

黑豆乳-牛乳混合奶酪成熟期间理化特性的研究

本文在黑豆乳-牛乳混合奶酪成熟期间,每隔5d测定理化指标,研究其成熟过程中理化特性的变化情况。研究结果表明:水分含量在成熟前期逐渐下降,后期基本维持在59%左右;酸度呈先增加再减少的趋势;内外部p H值呈上升趋势,且外部p H值比内部p H值高;p H 4.6可溶性氮、12%TCA可溶性氮、游离氨基酸含量和游离脂肪酸含量总体都呈明显上升趋势。     

崂山奶山羊乳的热稳定性影响因素研究

本文以崂山奶山羊乳为研究对象,对山羊乳的一般理化性质进行分析,并重点探讨了山羊乳的热稳定性。采用热凝固时间法(HCT)测定不同泌乳期、温度、pH值及相关助剂对山羊乳热稳定性的影响。结果表明,山羊乳的pH接近中性、酸度为11~23°T,且与泌乳期呈正相关关系。羊乳的稳定性随泌乳期的延长而增强,随加热温度的升高而急剧减弱。pH对羊乳的热稳定性影响较大,pH越大,HCT值越大,当待测乳样的pH值超过6.5时,乳样不再发生沉淀。在pH=6.0、140℃加热条件下,加入适量浓度为0.01~0.20mol/L的柠檬酸盐、磷酸盐、EDTA均可改善羊乳的稳定性,且添加物浓度越大,改善效果越好。添加钙离子亦可改变羊乳的热稳定性,其稳定性随钙离子浓度的升高而降低。羊乳热稳定性随蔗糖浓度的增大呈现出先升高后降低的趋势,添加浓度为35%的蔗糖时,待测羊乳的HCT值最高,羊乳的热稳定性最好。     

添加超滤牛乳的拉斯干酪特性

拉斯干酪添加有超滤牛乳制得,该牛乳中乳固形物质量分数分别为对照样(纯牛乳)的1.4、1.6和2.0倍,成熟3个月.拉斯干酪显示了比对照样更高的干酪得率,其水分、脂肪质量分数和pH值与对照样的相似,在成熟期均呈下降趋势,但氮质量分数等均呈上升趋势,且以牛乳中乳固形物质量分数提高到对照样的1.6倍时最高.结果表明,乳固形物质量分数为对照样1.6倍时牛乳制得的拉斯干酪其感官特性最佳.     

山羊奶对酸奶贮存过程中微生物学质量和粘度的影响

山羊奶和牛奶中加入奶粉 (1% ,2 %或 3%或不加 )所制成的酸奶样品。与牛奶 (11.75% )相比山羊奶干物质含量较低 (10 .72 % ) ,但干物质中蛋白、脂肪和灰分含量较高。山羊乳培养时间比牛乳大约长 50ｍｉｎ ,前者持续约 5.4ｈ。在 8℃、9天贮存期间 ,监测滴定酸度、ｐＨ值、粘度及乳杆菌和链球菌活菌计数的变化。与牛乳制成的酸奶相比 ,山羊乳酸奶具有柔软的稠度和较低的粘度 ,整个贮存期山羊乳酸奶也有较高的酸度。在山羊乳和牛乳酸奶样品中加入奶粉伴随着滴定酸度增加 ,加入奶粉也增加两种酸奶的粘度 ,特别是牛乳酸奶。贮藏期中粘度没有较大…     

薄膜蒸发浓缩对乳蛋白浓缩物加工性质的影响

乳蛋白浓缩物(Milk protein concentrate,MPC)是近年来新兴的牛乳蛋白制品,在食品加工中有着广泛的应用。本试验采用薄膜蒸发浓缩牛乳超滤截留液至固形物含量为15.55%,18.17%和26.12%,研究了不同浓缩程度对MPC粉末的粒径,溶解性,流动性和喷流性指数等性质的影响。结果表明,浓缩至超滤截留液固形物含量为26.12%时,MPC具有较好的加工特性。     

中甸和甘南牦牛乳中氮的分布

对云南中甸、甘肃甘南二个品种牦牛乳的基本组成、氮分布及氨基酸质量分数进行了研究.结果表明,中甸牦牛乳的平均组成为脂肪5.16%、蛋白质4.37%、乳糖4.58%、总固形物14.68%(均为质量分数);甘南牦牛乳的平均组成为脂肪7.56%、蛋白质5.32%、乳糖5.34%、总固形物17.76%.均高于荷斯坦牛乳.中甸和甘南牦牛乳的氮分布中,NPN分别为0.50和0.15 g/100g、NCN分别为1.31和1.23g/100g、WPN分别为0.81和1.08 g/100g、CN分别为3.06和4.09 g/100g都要高于牛乳.但中甸和甘南牦牛乳酪蛋白在总氮中所占的比例分别为70.02%和76.88%,低于牛乳的78.40%.中甸和甘南牦牛乳的氮分布存在明显的差异.从氨基酸的评分看牦牛乳的氨基酸评分和化学评分均高于牛乳,说明牦牛乳蛋白质的营养值高于牛乳.     

冻结方式对凡纳滨对虾贮藏中组织冰晶及品质的影响

新鲜凡纳滨对虾采用液氮、平板及冰柜冻结结合-20 ℃贮藏,研究不同贮藏时间内其组织冰晶形态与品质变化,以评价出最优的冻结方式。结果显示,随着贮藏时间的延长,平板及冰箱冻结的盐溶性蛋白含量、持水性、感官评分显著降低(p<0.05);而液氮冻结形成的冰晶直径比平板速冻小1/3,比冰箱小1/2;冻结后贮藏180 d其挥发性盐基氮(TVB-N值)≤25 mg/100 g,硫代巴比妥酸值(TBA)仅为0.72 mg/100 g,有效抑制了虾肉肌原纤维蛋白变性及脂肪氧化,能较好维持肌肉组织形态和品质,从而使虾肉的货架期延长至180 d以上。     

A survey of the physicochemical and microbiological quality of ultra‐heat‐treated whole milk in Brazil during their shelf life

The objective was to evaluate the quality of important brands of ultra‐heat‐treated (UHT) milk marketed in the northern of Parana State, Brazil, during the shelf life of the product. Five brands were analysed at 30, 60, 90 and 120 days after UHT milk production. The physicochemical quality of the milk was assessed in terms of fat content, titratable acidity, density, freezing point depression, total solids, solids‐not‐fat, proteolysis and alcohol stability. Microbiological quality was assessed by the enumeration of aerobic mesophilic micro‐organisms. None of the brands complied with all the physicochemical standards. Two brands met all applicable microbiological requirements. Gelation was observed from 90 days of storage onwards in all brands.     

不同冻结方式对金鲳鱼水分、组织结构与品质变化的影响

为研究不同冻结方式对金鲳鱼水分、组织结构与品质变化的影响,本实验以鲜活金鲳鱼为原料,分别采用平板冻结（plate freezer,PF）、螺旋式冻结（spiral freezer,SF）、超低温冻结（cryogenic freezer,CF）和冰柜冻结（ordinary freezer,OF）处理样品,随后通过pH值、挥发性盐基氮（total volatile basis nitrogen,TVB-N）含量、质构特性、色泽、保水性（持水率、蒸煮损失率和汁液损失率）等指标,并结合低场核磁共振与光学显微镜观察,综合评价4 种冻结处理方式对冷冻金鲳鱼水分、组织结构与品质变化的影响。结果发现：整体而言,SF组样品的指标均优于OF组,CF组样品与SF组样品的pH值和TVB-N含量较低,其质构、色泽与保水性变化速率低于PF与OF组。由低场核磁共振结果可知,SF处理对样品水分流失影响最小。由肌肉组织微观结构观察可知,CF组与SF组样品肌原纤维间隙小、分散均匀,组织冰晶细小,金鲳鱼的综合品质较好。因此,与其他冻结方式相比,SF处理的综合效果最佳。     

Analysis of tomato fruit: Effect of frozen storage on compositional values—an inter-laboratory study

Tomato culturing trials often result in too many samples to analyse while fresh. The most common technique is to seal them in containers and preserve them by deepfreezing for subsequent analysis. An inter-laboratory study has been made of the effect of freezing for various lengths of time on a number of compositional factors. Tests for soluble solids, dry matter content, electrical conductivity, titratable acidity, potassium, pH, glucose, fructose, sucrose, total N and Vitamin C in frozen tomatoes indicated that the levels of most of these constituents remained relatively constant during frozen storage and were similar to values found in the fruit prior to freezing. When the tomatoes were frozen as a purée it was essential to thaw them in the stabilising/ extracting solution used in the Vitamin C analytical procedure, otherwise there was a large loss in ascorbic acid.     

Effect of freezing time on the quality of Indian mackerel (Rastrelliger kanagurta) during frozen storage

The present study aims to find the effect of freezing methods on the quality of mackerel (Rastrelliger kanagurta) in commercial plate and air blast freezers during freezing and subsequent frozen storage (-18 degrees C). Total time for freezing was significantly different (P < 0.05) between the plate and air blast freezers (90 and 220 min, respectively). This difference in the freezing time could be attributed to the varied quality of the 2 samples. Upon freezing, the moisture content decreased in air blast frozen samples compared to plate freezer where protein content decreased in both the samples. Upon freezing and during frozen storage, lipid oxidation products (peroxide value, thiobarbutiric acid value, and free fatty acid value) and volatile bases (total volatile base nitrogen and trimethyl amine nitrogen) showed an increasing trend in both the samples with values slightly higher in air blast frozen samples compared to plate frozen samples. The total plate counts showed a significantly (P < 0.05) decreasing trend in both the samples. K value did not show any significant (P < 0.05) difference between the samples where as the histamine formation was significantly (P < 0.05) increased in air blast frozen samples compared to plate frozen samples. The taste and overall acceptability was significantly different (P < 0.05) in plate frozen samples compared to air blast frozen samples on 3rd month. Both samples were in acceptable condition up to 3 mo but the plate frozen samples quality was slightly better than the air blast frozen samples.     

Physicochemical and volatile profile alterations in pasteurized and frozen strawberry pulp during storage

This study evaluated the physicochemical characteristics and volatile profile of strawberry pulp subjected to factors, pasteurization (unpasteurized and pasteurized), freezing method (static air and forced air), and their interactions, during 12 months. Strawberry fruit were washed, sanitized, and pulped. The pulp was packaged, pasteurized, and frozen (0, 2, 4, 6, and 12 months). We concluded that pasteurization alters the strawberry pulp color. The impact of pasteurization and freezing method on the strawberry pulp pH, titratable acidity, and soluble solids variables is negligible. We tentatively identified 13 volatile compounds in fresh fruit and pulp, ethyl acetate, ethyl hexanoate, and linalool being the volatiles with the highest area percentage in the two products. The esters were predominant in both the fruit and strawberry pulp. Time is the most determining factor in modifying the strawberry pulp volatile profile, having an isolated effect on the increase of ethanol, ethyl butanoate, and linalool.

Practical applications

The strawberry is very used worldwide as raw material to different products, due to its color, flavor, and aroma. Thus, obtaining further information about the changes caused by processing and storage is of great importance for the food industry. This study shows the effect of simultaneous application of different processing techniques (pasteurization and freezing methods) on physicochemical variables and volatile profile of strawberry pulp over prolonged storage. Significant and unpublished results involving color, pH, acidity, soluble solids, and volatile compounds of strawberry frozen pulp over storage period are presented and may be applied for food industry to keep the pulp quality.     

抗坏血酸盐浸渍冷冻对东北冻梨食用品质的影响

目的探究抗坏血酸盐浸渍冷冻处理对冻梨果实食用和营养品质的影响。方法以南果梨为试验材料,分别采用0.5、1.0、3.0 g/L异抗坏血酸钠和0.5、1.0、3.0 g/L抗坏血酸钙溶液进行浸渍冷冻,对制得冻梨果实的色泽、褐变程度、可溶性固形物含量、可滴定酸含量、感官评价、石细胞含量、抗坏血酸含量和总酚含量进行分析。结果与空白组相比,异抗坏血酸钠与抗坏血酸钙溶液浸渍冷冻均可有效改善冻梨果实的色泽,抑制其褐变程度,维持其可溶性固形物含量,提高可滴定酸、抗坏血酸和总酚含量,并降低其石细胞含量,维持其较高的感官品质。结论抗坏血酸钙质量浓度为3.0 g/L时所得冻梨品质最优,为传统东北冻梨加工方式提供了技术支撑。     

FREEZE CONCENTRATION BY DIRECTIONAL COOLING

ABSTRACT— It is generally assumed that as food materials are frozen, soluble solids move ahead of the "ice front.' Under conditions tested in these studies the above was true only when the ice front moved in a descending direction. Thus, when foods were frozen in an ascending direction (as on a plate freezer) there was little, if any, movement of solids. When the freezing surface was placed above the material to be frozen, there was a rapid downward movement of solids. This "solids descent' was most apparent in true solutions such as drinks, and less apparent in structural cellular foods such as pieces of meat or potatoes. It is suggested that this phenomenon may be utilized for more efficient freeze drying or concentrating, or for the simultaneous production of low-solids and concentrated foods, particularly beverages.     

The effect of inulin as a fat replacer on the quality of set-type low-fat yogurt manufacture

The influence of different levels of inulin on the quality of fat-free yogurt production was investigated. Inulin was added to milk containing 0.1% of milk fat to give inulin levels of 1, 2 and 3%. The experimental yogurts were compared with control yogurt produced from whole milk. The total solids content of milk was standardized to 14% by adding skim milk powder to the experimental yogurt. The chemical composition, pH, titratable acidity, whey separation, consistency, acetaldehyde and volatile fatty acidity contents were determined in the experimental yogurts after 1, 7 and 15 days. Sensory properties of the yogurts were evaluated during storage. The addition of inulin at more than 1% increased whey separation and consistency. Acetaldehyde, pH and titratable acidity were not influenced by addition of inulin. Tyrosine and volatile fatty acidity levels were negatively affected by inulin addition. With respect to the organoleptic quality of yogurt, inulin addition caused a decrease in organoleptic scores: the control yogurt had the highest score, and the lowest score was obtained in yogurt samples containing 3% of inulin. Overall, the yogurt containing 1% of inulin was similar in quality characteristics to control yogurt made with whole milk.