原料奶中产生的不良风味及其控制技术措施

原料奶风味已成为衡量原料奶质量的一项重要指标,原料奶中产生的不良风味不仅会影响奶户交奶和奶企收奶,而且还会影响消费者的口感,同时也会降低牛奶的营养价值。本文主要通过对原料奶中的固有良好风味和不良风味及其来源进行分析,并从整体上提出控制原料奶中产生不良风味的技术措施,为生产优质风味奶和奶制品提供技术保障。     

不同养殖模式下罗非鱼养殖水体异味物质的含量及其变化

为获知不同罗非鱼养殖方式下水体中异味物质组成及含量变化,于2013年5月、8月和10月期间对海南文昌1座水库和6处全投料精养池塘,以及广东茂名3座水库、6处全投料精养池塘和6处立体养殖池塘(罗非鱼和家猪立体养殖)的养殖水体进行采样,利用吹扫捕集结合气相色谱-质谱联用技术(PT-GC-MS)对水体主要土腥味物质:土臭素(geosmin,GSM)和二甲基异莰醇(2-methylisoborneol,2-MIB)进行定量分析检测。结果发现:2-MIB为两地养殖水体中主要致嗅物质,含量为0~65.61μg/L;少量采样点检出GSM,含量为0~11.77μg/L。在3种养殖模式(水库、精养池塘和鱼猪立体养殖池塘)中,两种异味物质的分布均为水库最低,精养池塘次之,鱼猪立体养殖池塘最高,且两两之间存在显著差异(P0.05)。不同养殖时间及养殖地区间异味浓度差异不显著。结果表明,养殖模式会对养殖水体的异味物质含量造成影响,鱼猪立体池塘养殖模式的异味物质来源复杂,更易产生严重的土腥味。     

电化水去除淡水鱼土腥味的研究

为改善淡水鱼土腥味严重导致品质下降的现状,实验从淡水鱼终端暂养环节出发,以电化水暂养淡水鱼,探讨去除土腥味效果和实用性。结果显示,电化水通过比常规水体更小的水分子团簇结构以及更低的粘度、更强的渗透性和溶解力等理化性质实现鱼肉土腥味物质的快速脱除,暂养淡水鱼24 h可去除64.66%以上土臭素(Geosmin)和24.45%以上二甲基异莰醇(2-Methylisoborneol),相比井水分别提高136.65%、196.13%以上。     

罗非鱼不同养殖系统对产出效果及异味物质含量的影响

对鱼菜共生系统、底排污系统、底排污+鱼菜共生3种养殖系统的水质变化和罗非鱼产出效果进行了分析,并利用微波蒸馏-吹扫捕集-气相色谱质谱联用技术检测了各系统水体中和罗非鱼肌肉中异味物质的含量变化。经过12周的养殖实验,对终重、生物量、特定生长率、饵料系数、增重率等指标进行测量比较,结果发现,罗非鱼的产出效果从优到差依次为:鱼菜共生组、底排污+鱼菜共生组、底排污组、对照组;底排污+鱼菜共生系统水体中溶解氧在各时期均最高,其亚硝氮、氨氮含量在各时期均最低;底排污或鱼菜共生系统均能有效降低养殖水体中异味物质2-MIB和GSM含量;对照组罗非鱼肌肉中异味物质含量最高,2-MIB和GSM分别达到(0.67±0.02)μg/kg和(0.870±0.018)μg/kg,而底排污+鱼菜共生组罗非鱼肌肉中异味物质含量在各时期最低,2-MIB和GSM分别为(0.31±0.02)μg/kg和(0.53±0.042)μg/kg。结果表明,在罗非鱼精养池塘中,可通过底排污和鱼菜共生结合,降低水体中和罗非鱼体内异味物质的累积,提高其经济价值。     

Evaluating the microbial effects of stocking freshwater snails (Physa gyrina) in water reuse systems culturing rainbow trout (Oncorhynchus mykiss)

A study was conducted to analyze the effects of snails (Physa gyrina) on biofilm, bacterial abundance, off-flavor-producing bacteria, and off-flavor compounds in reuse aquaculture systems culturing rainbow trout (Oncorhynchus mykiss). Eight experimental-scale systems were used, including four with and without snails. Mean heterotrophic bacteria counts in water were lower (P < 0.05) in systems with snails. Submerged surfaces of sumps containing snails were nearly biofilm-free, while sumps without snails were coated with biofilm. Geosmin levels in trout fillets from snail-stocked systems were generally lower but not statistically different from the controls. Rainbow trout health and performance was not affected by snail presence.     

L-肉毒碱对鲤异味、生长、身体组成和某些生化指标的影响

选用初体重25．74-33．53g的正常健康鲤,经α-二甲基异莰醇(2-methylisobomeol,MIB)人工染味后,用含L-肉毒碱分别为0、50、100、150、200、250mg／kg的配合饲料投喂60d。结果表明：用添加了L-肉毒碱的饲料投喂鲤,可以明显去除人工染味鲤体内的异味,使之达到人的味觉能接受的程度;鲤摄食含L-肉毒碱100mg／kg的饲料后,可显著促进其生长;摄食添加L-肉毒碱饲料的鲤,其血液中超氧化物歧化酶(SOD)的活性明显比对照组鱼的高,而谷丙转氨酶(GPT)的活性明显比对照组鱼的低,说明L-肉毒碱可减缓MIB对鲤的伤害。     

辐照金皇后瓜汁异味成分分析

采用固相微萃取SPME方法对1，3和5kGy^60Co辐照处理的冷冻金皇后瓜汁挥发成分进行萃取富集，并结合GC-MS联机检测，发现金皇后瓜汁辐照后酯类挥发物峰面积由未辐照处理前的75．15％，分别减少到25．05％，14．47％和14．02％，而辐照金皇后瓜汁中的醇类和酮类则有一定程度的增加。金皇后瓜汁经不同辐照剂量处理后产生了较多的C6～C9醇和醛类，它们是不饱和脂肪酸的氧化产物，不稳定，多呈脂肪味，它们峰面积的变化较大，香气阈值较低，是构成金皇后瓜汁辐照异味的重要成分。     

鲤土腥味的感官检测与实践

利用食品感官检测的方法对鲤Cyprinus carpio L土腥味进行了检测试验,确定了土腥味感官评分与实际含量之间的对应关系,制定了对土腥味感官评价的评分标准,并应用此标准,研究了水中土腥味含量对鱼体土腥味的影响。     

Effect of ethanol, clofibric acid and temperature on the uptake and elimination of 2-methylisoborneol in channel catfish (Ictalurus punctatus)

Off-flavor, due to organoleptic compounds such as 2-methylisoborneol (MIB), is the single largest detriment to the harvest, production and profit from the channel catfish aquaculture industry of the Southeastern United States. Methods to increase the metabolism and/or elimination of compounds like MIB would provide a means towards improving catfish rearing practices. Previous studies indicated one or more forms of cytochrome P450 monooxygenase (CYP) may be involved in the biotransformation and elimination of specific organoleptic compounds, such as 2-methylisoborneol (MIB). In order to determine the role of CYP in the elimination of MIB, various compounds that have been shown to modulate cytochrome P450 expression in catfish were administered before and after exposure to ¹⁴C-MIB. Uptake and elimination was monitored in fish over 24 and 48 h, respectively. Pretreatment with clofibric acid (100 mg kg^–1-gavage) which induces a CYP2K-like isoform, and ethanol (1.0% v/v-aqueous) a CYP2 represser, alone and with enhanced temperature (added 10 °C) failed to affect uptake of MIB. Pretreatment with these compounds and conditions also failed to enhance elimination of MIB from channel catfish. However, when fish were treated with 1.0% ethanol after MIB exposure (i.e., during depuration), beta elimination halflives were changed from 144±35 to 71±13 h. in sexually mature animals but unchanged (191±113) in juveniles. The failure of CYP-modulating agents to alter MIB elimination in catfish suggests MIB may not readily undergo Phase I oxidation via CYP. The enhanced elimination of MIB in adults by ethanol warrants further study as to its potential use in aquaculture in purging MIB and related compounds prior to fish processing.