真空包装牡蛎肉在冷藏和冻藏过程中的品质变化

为研究真空包装牡蛎肉在4℃冷藏和-18℃冻藏过程中品质的变化规律,以感官评分、白度、亮度L*、蒸煮损失率、pH值、挥发性盐基氮(total volatile basic nitrogen,TVB-N)、硫代巴比妥酸(thibabituric acid,TBA)值、菌落总数为评价指标,分析其新鲜度。结果表明:真空包装牡蛎肉在冷藏与冻藏贮藏条件下,感官评分、白度和L*均随贮藏时间的延长而降低,其中冻藏牡蛎肉的变化趋势较缓慢;TVB-N值随着贮藏时间的延长而升高,且冷藏组显著高于冻藏组(p 0.05)。TBA值和p H值均不能独立反映牡蛎的新鲜度,需结合其它指标对牡蛎品质进行综合评价。冷藏牡蛎肉的菌落总数随贮藏时间延长而增加,冻藏组随贮藏时间延长而减少。相关性分析表明,除pH值外,其它检测指标均可作为冷藏、冻藏牡蛎肉新鲜度评价的有效指标。     

微冻和冷藏对牙鲆贮藏品质的影响

以感官、理化和微生物为指标,研究了微冻(-2℃)和冷藏(4℃)对牙鲆品质变化及货架期的影响。结果表明,随着贮藏时间的延长,牙鲆鱼的感官品质显著下降(p0.01),菌落总数、挥发性盐基氮(TVB-N)含量、硫代巴比妥酸(TBA)值和K值均呈显著上升趋势(p0.01),且微冻贮藏时各指标的变化速率都低于冷藏;质构特性中的硬度、弹性、咀嚼度和粘聚性随贮藏时间的延长而显著下降(p0.05),p H与贮藏时间及其他理化指标(TBA除外)相关性不显著。综合感官评分、TVB-N值及菌落总数等指标得出牙鲆在4℃和-2℃贮藏条件下的货架期分别为9 d和12 d。与冷藏相比,微冻能更有效地抑制微生物的生长,延长其货架期。     

不同水分含量鲜腐竹冷藏过程中品质变化研究

目的 探究不同初始水分含量下鲜腐竹冷藏过程中品质的变化规律,确定适宜鲜腐竹冷藏的初始水分含量。方法 将鲜腐竹干燥至水分含量分别为50%、45%、40%后,4℃冷藏。利用色差计、质构仪（texture profile analysis,TPA）)、扫描电镜（scanning electron microscope,SEM）、低场核磁共振（low-field nuclear magnetic resonance,LF-NMR）测定鲜腐竹的色泽、质构特性、微观结构和水分分布状态;采用化学分析手段测定鲜腐竹的可溶性肽含量、过氧化值、蒸煮损失率,并对鲜腐竹进行感官评分和菌落总数测定,探究冷藏过程中鲜腐竹的品质变化规律以及水分含量对鲜腐竹冷藏品质的影响机制。结果 随着冷藏时间的延长,鲜腐竹的L*值呈下降趋势,a*值、b*值呈增加趋势,鲜腐竹感官品质劣变,蒸煮损失率、可溶性肽含量、过氧化值含量、菌落总数增加。初始水分含量下降,腐竹色泽L*值降低,a*值增加;40%和45%水分含量的腐竹,冷藏过程中的硬度、胶黏性、咀嚼性较高,45%水分的腐竹弹性最大,且质构特性更为稳定;冷藏过程中,鲜腐竹感官品质劣变,降低水分含量至45%和40%时,可使鲜腐竹在第8d时感官评分在60分以上,其对感官品质中的质地和气味改善最大;40%的初始水分含量,腐竹的蒸煮损失率最低,但与45%的水分含量不具有显著性差异(P<0.05);降低水分含量,可延缓鲜腐竹最大过氧化值出现的时间,降低蛋白质网络结构的破坏程度。冷藏过程中存在明显的水分迁移现象,鲜腐竹的硬度、咀嚼性、弹性、胶黏性受可溶性肽含量影响最大,与其呈极显著负相关（P<0.01）。结论 初始水分含量显著影响鲜腐竹的冷藏品质,降低水分含量对于延长鲜腐竹保质期具有重要意义。     

不同压力处理大米制得米饭冷藏期间的品质变化

研究了冷藏条件下不同压力处理大米制得米饭品质的变化。大米在温度40℃、米水比(m/m)1:2的条件下浸泡40 min,并在15℃下分别经200、400、600 MPa处理10 min,浸泡后未经超高压处理的大米为对照试验组,随后蒸煮15 min制成米饭,保鲜膜密封后置于4℃下贮藏7 d,每天对米饭品质相关指标进行测定,并与感官鉴评结果比较。结果表明:超高压米饭的硬度上升较缓慢;黏着性、碘蓝值、p H下降均较快;透光率、白度(W)的上升均较快。400、600 MPa米饭水分含量的变化幅度较大。贮藏期间,200 MPa米饭的W和碘蓝值均最高,p H值最低,感官评分较低。400 MPa米饭的硬度、p H值和W均较低,感官评分接近对照。600MPa米饭的硬度较高,W较低,碘蓝值的下降和透光率的上升均最快,感官评分最低且下降速率最快。总体来说,大米200、400、600 MPa处理对米饭冷藏品质的影响都是弊大于利。     

解冻方式对近江牡蛎肉感官特征和理化指标的影响

为获得冻结牡蛎肉的最佳解冻方式,以解冻时间、感官评分、质构、色差、解冻损失率、蒸煮损失率、pH、挥发性盐基氮(Total volatile basic nitrogen,TVB-N)、硫代巴比妥酸(Thibabituric acid,TBA)和菌落总数为指标,研究自然解冻、静水解冻、冷藏解冻、超声波解冻和微波解冻5种解冻方式对近江牡蛎感官特征和理化指标的影响,并采用变异系数权重法对解冻后牡蛎肉品质进行综合评价。结果表明:自然解冻(128 min)与冷藏解冻(309 min)所需时间较长,解冻后牡蛎肉的感官评分最小,分别为4.6、4.4分;TVB-N、TBA和菌落总数较大。微波解冻(1.5 min)和超声波解冻(9 min)耗时较短,感官评分较高,分别为6.12、6.0分;TVB-N、TBA和菌落总数最小,但蒸煮损失率和解冻损失率较大。静水解冻所需时间31 min,感官评分(6.0分)较高,但TVB-N、TBA和细菌总数较大。综合评价结果显示,解冻时间(权重值为0.357)对牡蛎肉品质影响最大,微波解冻综合评分(0.548)最高,是理想的近江牡蛎肉解冻方式,但持水力较低,微波解冻条件仍需进一步研究。     

真空预冷对青菜贮藏品质的影响

本实验选取叶类蔬菜——青菜为研究对象,研究了真空预冷过程中青菜温度、真空室压力随时间的变化规律及贮藏过程中青菜品质的变化。实验结果表明:青菜预冷至4℃,整个过程不到300s;真空预冷对青菜冷藏过程中的品质具有积极的正向作用,能够有效抑制青菜贮藏过程中感官品质的下降,减缓VC、叶绿素的降低,并抑制亚硝酸盐含量的升高,保持MDA含量在较低的水平。     

对比PE膜与微孔膜对冷藏青萝卜品质的影响

为探讨包装材料对青萝卜采后贮藏品质的影响,以卫青萝卜为试材,在(2.0±0.5)℃冷藏条件下,分别采用PE膜、微孔膜对卫青萝卜进行包装,比较了卫青萝卜主要理化及感官指标变化。结果表明:贮藏期间PE膜组和微孔膜组的VC、酸度、可溶性固形物、亚硝酸盐以及还原糖含量变化基本一致,均为先上升后下降。微孔膜组的VC含量、酸度、可溶性固形物含量和失重率均比PE组高;PE组的淀粉酶活性、还原糖和亚硝酸盐含量高于微孔膜组;微孔膜组的质构指标和感官指标优于PE组;二者色差指标差异不明显。微孔膜包装处理的卫青萝卜最佳食用期为5周,最佳贮藏期为11周。PE组包装处理的卫青萝卜品质随着贮藏时间的延长而逐渐下降,最佳贮藏期为9周。微孔膜组的卫青萝卜品质更佳。     

臭氧冷海水对竹筴鱼冷藏品质的影响

为了分析臭氧冷海水处理对冷藏竹筴鱼品质的影响,本文研究了自来水预处理(A)、冷海水预处理(B)、臭氧冷海水预处理(C)的竹筴鱼在4±1℃贮藏条件下的鱼体菌落总数(APC)、p H值、挥发性盐基氮(TVB-N)、硫代巴比妥酸值(TBARS)、色差、质构和感官品质的变化规律。结果显示,在贮藏期间,各预处理竹筴鱼鱼体的菌落总数、TVB-N和b*均随着冷藏时间的延长而上升,在贮藏后期B和C处理对鱼体菌落总数和TVB-N的抑制作用显著高于A处理,且C处理效果显著好于B处理(p0.05)。第10天时,A组鱼体的菌落总数和TVB-N分别达到7.13 log CFU/g和31.43 mg/100 g,超出国家限定标准。同时,竹筴鱼的感官评分随着贮藏时间延长而下降,但B和C组较A组感官评分下降得慢。然而,B和C组鱼体脂肪氧化程度较A组高,说明臭氧和冷海水处理促进了鱼体脂肪的氧化。臭氧冷海水处理对p H值、色度的L*、a*值、质构影响不大。因此,臭氧冷海水处理有利于延缓竹筴鱼鲜度指标的下降,保证竹筴鱼的冷藏品质,延长其货架期。     

超高压处理对冷藏鲈鱼品质的影响

研究了不同超高压条件(0、100、200、300 MPa,保压处理10 min)对鲈鱼冷藏过程中感官、p H值、白度、质构特性和持水性的影响。结果表明:鱼肉的感官评分、硬度、弹性和咀嚼度随贮藏时间的延长逐渐降低,白度逐渐升高,p H值先下降后上升,而持水性先上升后下降。超高压处理可显著提高鱼肉的硬度和咀嚼度(P0.01),同时提高了鱼肉的p H值和持水能力,增加了白度,200 MPa处理组的细菌总数低于对照组和其他2个处理组。此外,300 MPa的超高压处理对鲈鱼鱼肉品质的影响最大。综合感官和理化测定结果可知,超高压在改善鲈鱼肉质方面具有潜在的应用前景。     

带鱼冷藏过程中品质变化与水分迁移的相关性

为了研究带鱼在冷藏期间的品质变化与水分迁移的关系,利用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)技术分析组织中水分变化规律。横向弛豫时间T_2的结果表明:随着贮藏时间的延长,不易流动水(T_(22))逐渐降低,自由水(T_(23))逐渐升高,肌原纤维内的水向外移动而大量流失,肌肉的持水能力下降、肉质逐渐劣化。这与传统理化指标的研究结果一致,且相关性分析表明,T_(22)、T_(23)与水分含量、蒸煮损失率等指标极显著相关(P0.01),与感官评分、持水力、硫代巴比妥酸值显著相关(P0.05)。因此,可考虑运用LF-NMR技术检测带鱼在冷藏期间的品质变化。     

Effects of Production and Processing Factors on Major Fruit and Vegetable Antioxidants

ABSTRACT: Public awareness of the purported health benefits of dietary antioxidants has increased the demand for fruit and vegetable products with recognized and improved antioxidant quality and has created new opportunities for the horticulture and food industry to improve fruit and vegetable quality by enhancing antioxidant content. This review describes the production and processing factors that influence the content of the major fruit and vegetable antioxidants, namely vitamin C, carotenoids, and phenolics. There is substantial genetic variation in the content of each of these antioxidant types among fruit and vegetable cultivars. Compared with vitamin C and carotenoids, the levels of phenolic antioxidants appear to be more sensitive to environmental conditions both before and after harvest. Although vitamin C can be readily lost during fresh storage, the content of certain carotenoids and phenolics can actually increase during suitable conditions of fresh storage. Vitamin C and phenolics are more susceptible to loss during processing, especially by leaching from plant tissues into processing water. The combination of cultivar variation and responsiveness to specific environmental conditions can create opportunities for the production and processing of fruits and vegetables with improved antioxidant properties.     

不同包装方式调理牛排在冰温贮藏过程中品质变化特点

本试验旨在为调理牛排的贮藏保鲜提供数据参考,以生鲜牛里脊为原料,经整形、腌制等工艺制成调理牛排,并对其进行托盘包装和真空包装,将包装后的成品贮藏于0~4 ℃及0~-1.5 ℃两种环境下,即托盘组冷藏条件(ST)、真空组冷藏条件(SZ)、托盘组冰温条件(BT)以及真空组冰温条件(BZ),并定期检测汁液流失率、感官评价、感官总评分、TBARS值、菌落总数、TVB-N值以及pH指标变化。结果表明:托盘包装下,BT组的货架期为20 d,与ST组的12 d相比能将货架期延长8 d;真空包装下,BZ组贮藏的货架期为32 d,与SZ组的20 d相比将货架期延长了12 d。在同种贮藏温度下,除汁液流失指标外,真空组各项指标变化幅度都低于托盘组,能够较好的维持调理牛排的品质;在贮藏期间,真空包装方式下,汁液流失较严重,且显著高于托盘组(p<0.05);BT组色泽变化较缓慢,BZ组气味变化较缓慢。相关性分析发现,SZ组、BZ组以BT组,汁液流失率、感官总评分、TBARS值、菌落、TVB-N值以及pH与调理牛排的贮藏时间显著相关。ST组,仅感官评分、菌落总数以及TVB-N与调理牛排品贮藏时间显著相关。因此,在贮藏过程中,冰温贮藏和真空包装方式均能有效改善调理牛排品质,且两者结合效果改善效果更明显。     

Ascorbic Acid and 5-Methyltetrahyclrofolate Losses in Vegetables with Cook/Chill or Cook/Hot-Hold Foodservice Systems

The percent retention of vitamin C and 5-methyltetrahydrofolate in seven cooked vegetables was analyzed using HPLC and compared in simulated cook/chill vs cook/hot-hold hospital foodservices. Retention of vitamins after conduction and infra-red reheating was investigated. Vegetables reheated after one day of chilled storage had greater losses of both vitamins compared to those held at 72°C for 30 min, but better vitamin retention than vegetables held hot 2 hr. There was no significant difference in nutrient retention due to method of reheating. If warm-holding is restricted to < 90 min, vitamin retention in vegetables is likely to be higher in a cook/hot-hold foodservice than with a cook/chill system.     

Microbial and sensory quality of vegetables for soup packaged in different atmospheres

Fresh prepacked vegetables for soup have become very popular on the Italian market, since they are already peeled, cut, washed and ready-to-use. The packaging and the modified atmosphere can prolong their shelf-life and maintain their hygienic, physicochemical and sensory characteristics during storage at + 4°C. The hygienic and sensory quality was evaluated by analysing microbial growth and atmosphere composition at the moment of packaging and at the end or the shelf-life of vegetables prepacked in air on under modified atmospheres, and by determining the browning or blackening of parsley and the loss of carrot exudates. A large number of different groups of microorganisms was found in raw vegetables. In spite of this high starting concentration of microbial flora, the prepackaging systems investigated did not seem to significantly influence their growth during vegetable storage at +4°C. No pathogenic microorganisms were isolated from the prepackaged vegetables. The hygienic quality was similar in all packaging systems used. However, the vegetables packaged in perforated. film kept their sensory characteristics better than those packaged in air or under a modified atmosphere.     

Metabolism and nutrition of young children in a children's home

Certain parameters of protein and fat metabolism, as well as provision with vitamins A, B1, B2 and mineral substances (calcium, phosphorus and magnesium) were studied in infants aged 1-3 years, at the Tartu Children's Home No. 2. Simultaneously, the infants' nutrition and development were investigated. It was found that the mean parameters of the protein and fat metabolism were within the normal limits, however, vitamin A, B1, D and unsaturated fatty acids deficiency was recorded in the infants studied. Food imbalance, that was greater in spring, led to metabolic disorders, vitamin and mineral deficiency resulted in the infants' growth retardation. It is recommended that infants in the children's homes should be given higher amounts of vegetables, fruit, milk and vegetable oil rich in vitamins, and vitamins in concentrated form, in prophylactic doses.     

小麦粉储存湿度对面粉品质及其制作馒头品质的影响

研究通用中筋粉在常温(25℃),不同湿度(50%、65%、80%)条件下储存过程中面粉中水分含量、粗蛋白质含量、湿面筋含量、脂肪酸值等指标及其制作面团的酸度和馒头的感官品质的变化。实验结果表明,在湿度80%条件下,随着储存时间的延长面粉水分含量变化显著(p<0.05)。同一储藏时间,湿度越高,面筋含量越低。不同湿度(50%、65%、80%)条件下,面粉中的脂肪酸值都随储存时间的增加而增加(p<0.05)。不同湿度(50%、65%、80%)储存过程的面粉制作的发酵面团的酸度都呈现先降低后增加的趋势,制作馒头的感官评分呈现下降的趋势(p<0.05)。面粉在不同湿度(50%、65%、80%)储存过程中,储存30 d的面粉,醒发后面团酸度都显著下降(p<0.05);继续延长储存期,在湿度50%下的面粉制作的面团酸度有回升,但不超过原始的面团酸度,随储存湿度提高面团酸度增加明显;感官评分表明,储存环境湿度越高,面粉制作的馒头品质下降越快,湿度80%储存60 d后的面粉制成的馒头口感差。湿度50%存放120 d仍可用于加工馒头。结论:面粉储存过程中,湿度越大,面粉品质下降越快,进而影响到所制作的馒头品质。     

DISINFECTION OF SHREDDED SALAD INGREDIENTS WITH SODIUM DICHLOROISOCYANURATE

Raw salads are frequently subjected to hypochlorite wash to reduce microbial numbers, retard enzymatic activity and improve shelf-life of sensory quality. Hypochlorite dips significantly reduce the initial population of natural contaminants on lettuce. However, populations on treated and untreated samples are not significantly different after four days storage at refrigeration temperature. Increasing the level of free available chlorine does not improve the microbicidal effect.
In this study sodium dichloroisocyanurate (NaDCC) was used to disinfect salad vegetables. Though the principal salad vegetable used was butterhead lettuce, results show that the efficacy of NaDCC in reducing total aerobic mesophile levels varies with vegetable type. NaDCC gives an acid pH in solution and has significantly higher activity than sodium hypochlorite.
For longer term storage, preparation of lettuce which included a 30 min soak in NaDCC improved the microbiological quality of the produce at the end of the storage period. The microbial load on disinfected produce was between 0.62 and 0.98 log cycles lower than on lettuce prepared without a disinfection step for up     

Development of a Quality Index Method for Frozen Hake (M. capensis and M. paradoxus)

A quality index method (QIM) consisting of 9 parameters with a total of 17 sensory points was developed for frozen hake (M. capensis and M. paradoxus). The score sheet was divided into 2 parts. The 1st, including 7 parameters with up to 13 sensory points, was directly related to loss of quality during storage at ?20 °C. Multivariate analysis confirmed the relevance of these parameters for prediction of storage time. The 2nd part contained 2 additional parameters scoring up to 4 sensory points. These parameters are commercially important but not directly linked to storage time.     

水晶蜜柚和溪蜜柚贮藏期间果实不同部位品质变化

本文以云南瑞丽地区主要栽培的柚子品种水晶蜜柚和琯溪蜜柚为试材,研究两种柚子在贮藏期间果实不同部位可溶性固形物(TSS)、可滴定酸(TA)、V_C及感官风味的变化。结果表明:在整个贮藏期间,水晶蜜柚和琯溪蜜柚果蒂部、赤道部和果脐部TSS均先增大后减小,水晶蜜柚果蒂部TSS变化最大,贮藏至120 d,果蒂部、赤道部和果脐部TSS分别比其最大值下降55.35%、43.39%和39.36%。琯溪蜜柚果蒂部、赤道部和果脐部TSS下降比例差异不大。在整个贮藏期,两种柚子可滴定酸(TA)均先减小后增大再减小,V_C均呈下降趋势,且果蒂部变化幅度均较大,贮藏至120 d,水晶蜜柚三个部位TA和V_C变化幅度均大于琯溪蜜柚,水晶蜜柚果蒂部、赤道部、果脐部TA比贮藏前显著(p<0.05)降低63.44%、52.22%和50.00%,V_C分别比贮藏前显著(p<0.05)降低53.70%、44.84%和43.00%。通过感官评分可知,在贮藏过程中,水晶蜜柚三个部位感官评分下降幅度均大于琯溪蜜柚,最先出现感官评分大幅度降低,且果蒂部最先达到不可接受程度。综合分析,两个品种柚子果蒂部品质变化均最大,水晶蜜柚贮藏一个月内会提高果实品质,但随着贮藏时间延长,果实品质大幅度降低,琯溪蜜柚果实品质降低幅度相对较小。     

Kinetic Parameters for the Thermal Inactivation of Peroxidase and Lipoxygenase in Precooked Frozen Brassica Species

Thermal inactivation of peroxidase (POD) and lipoxygenase (LOX), both enzymes present in broccoli and Brussels sprouts, is required before freezing, to obtain high‐quality precooked frozen vegetables. Rate constants of a 1st‐order biphasic model for the heat‐labile and heat‐resistant POD and LOX isoenzymes were determined at different temperatures (75, 80, and 90 °C) and the corresponding activation energies were estimated using nonlinear regressions. In the case of Brussels sprouts, the activation energies for the resistant and labile fractions were 56.3 and 62.5 kJ/mol for POD and 63.7 and 65.8 kJ/mol for LOX, respectively. For Brussels sprouts, different precooking times were tested to analyze the effect of residual enzyme activity on quality parameters and sensory attributes, after a frozen storage of 4 mo at ?20 °C. A significant reactivation of enzyme activity after frozen storage was observed (especially in the case of POD) for short precooking times (<6 min) leading to low‐quality parameters at the interior zone of the vegetable. A precooking time of 6 min at 90 °C allowed an adequate inactivation of LOX and POD obtaining a high‐quality final frozen vegetable. A sensory analysis confirmed the global acceptability of the product. The obtained results are relevant to define the precooking stage conditions in the production of frozen cruciferous vegetables.