寿命可靠性计算在食品货架期分析中的初步应用

以市售灭菌乳为研究对象,应用Weibull Hazard Analysis(WHA)方法,通过对食品品质指标的分析,预测食品的货架期;同时,探讨寿命加速试验线性无偏估计法在灭菌乳货架期可靠性分析方面的初步应用,分别在25、30、35、40℃环境下恒温贮藏,并定期随机抽样进行感官检验和测定酸度。     

不同温度对调理鸡排低温贮藏品质特性的影响

为研究不同温度对调理鸡排低温贮藏品质特性的影响,本实验利用3 种不同的贮藏温度（4 ℃（冷藏）、－2 ℃（冰温贮藏）和－18 ℃（冷冻贮藏））对调理鸡排进行贮藏,并通过对贮藏期间调理鸡排菌落总数、颜色、持水力、质构特性等的测定以及扫描电子显微镜的观察,分析调理鸡排理化品质以及微观结构的变化情况。菌落总数分析结果表明,相比于冷藏,冰温贮藏可以将调理鸡排的货架期延长2 倍（从约4 d延长到约12 d）;理化品质分析结果表明,冰温贮藏条件下调理鸡排的持水力和质构特性都得到了更好的保持。此外,扫描电子显微镜的观察结果表明,冰温贮藏条件下鸡排的微观结构受到的损伤相较于冷藏和冻藏而言更小。虽然冷冻贮藏条件下鸡排的货架期较长（3 个月以上）,但是其持水力、质构、微观结构等品质下降也更快。而冰温贮藏在延长货架期的同时,也更好地保持了调理鸡排的品质特性。综上,本研究可为冰温贮藏在调理鸡排贮运过程中的应用提供理论参考。     

利用物理硬度模型和感官综合因子模型预测长茄货架寿命

目的 利用物理硬度模型和感官综合因子模型分析长茄感官指标、硬度指标与贮藏天数的相关性, 为建立长茄货架寿命预测模型提供理论依据。方法 通过长茄物理指标硬度值对时间经非线性拟合获得不同温度(10、30 ℃)下的指数函数方程,利用3T原理和威布尔危害分析法求得累计硬度(品质)损失值∑S,从而计算长茄在10、30 ℃经历不同时间所消耗的 ,并求得货架剩余寿命。结果 通过真实温度变化不同时间条件下长茄的实际感官评分、物理硬度值与预测模型计算值进行比较,相对误差小于10%。当长茄在(10、30 ℃)下由于温度变化造成货架寿命变化,通过10 ℃感官评分综合因子线性回归方程K=-0.851X+29.359,结合在两温度段下基于物理指标硬度的非线性拟合方程 ,可用于长茄货架寿命预测。 结论 两种模型相结合能有效预测长茄的货架期,长茄在30 ℃条件下模型预测货架寿命为4.01 d,10 ℃时的预测寿命为15.01 d。     

Microbiological characteristics and deteriorative changes of ‘k woka’ (a nigerian non-fermented maize dish) produced using potassium sorbate and various steaming treatment

‘Kwoka’ (a popular Nigerian non-fermented maize meal) was produced using steaming for either 30 or 60 min or a combination of potassium sorbate (KS) treatment with steaming for 60 min. Microbiological characteristics and chemical quality were investigated during production and storage, together with organoleptic and objective (firmness only) assessment of quality during ambient storage (30 ± 2°C). The slurry (ie before steaming) and 30 min steamed K woka showed more diverse genera of moulds and bacteria than K woka steamed for 60 min (with or without KS). The organisms isolated from the raw materials and product belonged to the genera Bacillus, Staphylococcus, Lactobacillus, Enterobacter, Klebsiella, Aspergillus and Fusarium. During storage Bacillus cereus, Lactobacillus delbrueckii, L leichmannii and Klebsiella pneumoniae predominated. Coliforms and fungi were not detected on day 0 in KS-treated and 60 min steamed K woka. Marked reductions in aerobic plate counts (APC) and in the population of the different bacterial groups were observed in all samples following steaming, These increased sharply within 1 day of storage, the highest (6.50 log cfu g^?1) APC occurring on day 3 in 30 min steamed K woka. Of the bacterial groups, the Lactobacillus population increased most markedly and this probably reflects the significant increase in acidity observed especially on day 6. Adverse quality changes in appearance, aroma and firmness were more apparent in the control (ie without KS treatment) and the samples were unacceptable after 1 day but the shelf-life of K woka produced using KS treatment and 60 min steaming was extended by 2 days.     

Suitability of high-dynamic-pressure-treated milk for the production of yoghurt

The aim of this work was to evaluate, using the response surface methodology, the effects of different levels of high-pressure homogenization (HPH) on the microbiological and rheological characteristics of yoghurts having different contents of fat and milk solids. The HPH treatment of milk resulted a useful tool to obtain yoghurts having a greater variety of textures associated to a high microbiological quality. In fact, all the yoghurt types obtained by using milk treated with different levels of pressure were characterized by cell loads of the starter cultures higher than 8 log₁₀ cfu ml⁻¹ immediately after the fermentation and than 7 log₁₀ cfu ml⁻¹ after 60 days of storage at 4°C. The HPH treatment seems to favor the growth of Streptococcus thermophilus with respect to that of Lactobacillus delbrueckii subsp. bulgaricus, regardless of the level of pressure applied. The use of a Central Composite Design (CCD) and the polynomial models obtained permitted to individuate the levels of the three independent variables (pressure level, milk solids and fat concentration) able to maximize the growth of starters during the fermentation process, to minimize their viability loss during the refrigerated storage as well as to define their effects on the product viscosity.     

Monte Carlo simulation model predicts bactofugation can extend shelf-life of pasteurized fluid milk,even when raw milk with low spore counts is used as the incoming ingredient

Bacterial spores from raw milk that survive the pasteurization process are responsible for half of all the spoilage of fluid milk. Bactofugation has received more attention as a nonthermal method that can reduce the presence of bacterial spores in milk and with it the spoilage of fluid milk. The objective of this work was to determine the effectiveness of bactofugation in removing spores from raw milk and estimate the effect the spore removal could have on shelf-life of fluid milk. The study was conducted in a commercial fluid milk processing facility where warm spore removal was performed using one-phase bactofuge followed by warm cream separation and high temperature, short time pasteurization. Samples from different stages of fluid milk processing with and without the use of bactofuge were tested for total plate count, mesophilic spore count, psychrotolerant spore count (PSC), and somatic cell count. Results were evaluated to determine the count reductions during different stages of fluid milk processing and compare counts in fluid milk processed with and without bactofugation. Bactofugation on average reduced the total plate count by 1.81 ± 0.72 log cfu/mL, mesophilic spore count by 1.08 ± 0.71 log cfu/mL, PSC by 0.86 ± 0.59 log cfu/mL, and somatic cell count by 135,881 ± 43,942 cells/mL. Psychrotolerant spore count in final pasteurized skim milk processed with and without bactofugation was used to predict the shelf-life of the pasteurized skim milk using the Monte Carlo simulation model. Although PSC in the initial raw milk was already low (?0.63 ± 0.47 log cfu/mL), the predicted values from the simulation model showed that bactofugation would extend the shelf-life of pasteurized skim milk by approximately 2 d. The results of this study will directly help fluid milk processors evaluate the benefits of using bactofugation as an intervention in their plants, and also demonstrate the benefits of using mathematical modeling in decision making.     

Production and storage stability of concentrated micellar casein

Concentrated micellar casein (CMC) is a high-protein ingredient that can be used in process cheese product formulations. The objectives of this study were to develop a process to produce CMC and to evaluate the effect of sodium chloride and sodium citrate on its storage stability. Skim milk was pasteurized at 76°C for 16 s and cooled to ≤4°C. The skim milk was heated to 50°C using a plate heat exchanger and microfiltered with a graded permeability (GP) ceramic microfiltration (MF) membrane system (0.1 μm) in a continuous feed-and-bleed mode (flux of 71.43 L/m² per hour) using a 3× concentration factor (CF) to produce a 3× MF retentate. Subsequently, the retentate of the first stage was diluted 2× with soft water (2 kg of water: 1 kg of retentate) and again MF at 50°C using a 3× CF. The retentate of the second stage was then cooled to 4°C and stored overnight. The following day, the retentate was heated to 63°C and MF in a recirculation mode until the total solids (TS) reached approximately 22% (wt/wt). Subsequently, the MF system temperature was increased to 74°C and MF until the permeate flux was <3 L/m² per hour. The CMC was then divided into 3 aliquots (approximately 10 kg each) at 74°C. The first portion was a control, whereas 1% of sodium chloride was added to the second portion (T1), and 1% of sodium chloride plus 1% of sodium citrate were added to the third portion (T2). The CMC retentates were transferred hot to sterilized vials and stored at 4°C. This trial was repeated 3 times using separate lots of skim milk. The CMC at d 0 (immediately after manufacturing) contained 25.41% TS, 21.65% true protein (TP), 0.09% nonprotein nitrogen (NPN), and 0.55% noncasein nitrogen (NCN). Mean total aerobic bacterial counts (TBC) in control, T1, and T2 at d 0 were 2.6, 2.5, and 2.8 log cfu/mL, respectively. The level of proteolysis (NCN and NPN values) increased with increasing TBC during 60 d of storage at 4°C. This study determined that CMC with >25% TS and >95% casein as percentage of TP can be manufactured using GP MF ceramic membranes and could be stored up to 60 d at 4°C. The effects of the small increase in NCN and NPN, as well as the addition of sodium chloride or sodium citrate in CMC during 60 d of storage on process cheese characteristics, will be evaluated in subsequent studies.     

A comparison of wet-extracted coconut oils prepared under hot and cold conditions

Virgin coconut oil was prepared by four wet extraction methods which included hot extraction by boiling coconut milk, and three cold extraction methods by centrifugation, fermentation, and chilling followed by thawing of coconut milk. The chemical characteristics related to both saponifiable and unsaponifiable fractions of oils were evaluated. Quality parameters such as peroxide value, iodine value, saponification value, acid value, and moisture content of the four oils remain within the acceptable range for edible purposes. Hot conditions incorporate a richer phenolic profile, a higher α-tocopherol content, and a higher β-carotene content in coconut oil. Epimerization and hydrolysis of the phenolic compounds occur depending on the extraction conditions. The longest shelf-life of the coconut oil prepared under hot conditions may be due to the relatively lower contents of moisture, free acids, peroxides, and higher contents of phenolic compounds, α-tocopherol, and β-carotene in hot-extracted coconut oil. Contrary to popular belief, hot and wet extraction conditions may produce higher quality coconut oil compared to cold extraction conditions.     

基于响应面法优化鲜切莴笋复合涂膜保鲜剂

以鲜切莴笋为研究对象,根据12种化学物质对多酚氧化酶(PPO)和过氧化物酶(POD)活性的抑制作用,选择3种酶活抑制效果显著的化学物质(茶多酚、抗坏血酸和L-半胱氨酸)和4种涂膜剂(羧甲基纤维素钠、黄原胶、海藻酸钠和葡甘露聚糖),考察不同保鲜剂浓度对鲜切莴笋4 ℃贮藏4 d后外观和色泽的影响. 以此单因素实验为基础,进行响应面分析,结果显示复合涂膜最佳组合为0.38%抗坏血酸+0.85%L-半胱氨酸+0.67%羧甲基纤维素钠,在此条件下,鲜切莴笋在4 ℃贮藏6 d后红绿色差Δa^*值为0.170,与回归方程预测值0.166相近,且货架寿命可延长至12 d以上,表明优化后的复合涂膜保鲜剂具有良好的实际保鲜效果.