Determination of trimethylamine nitrogen and total volatile basic nitrogen in fresh fish by flow injection analysis

There are many chemical, microbiological and sensory indices of fish quality. Of the chemical indices, TMA-N and TVB-N are probably the most used in connection with remaining shelf-life determination. This paper reports on a study of modifications to a flow injection analysis (FIA) method necessary to make it suitable for TMA-N and TVB-N determination, specifically the optimal concentrations of NaOH and formaldehyde for releasing the volatile bases from the acidic fish extract and sequestering the non-TMA volatile bases respectively. The effects of using perchloric acid (PCA) and trichloroacetic acid (TCA) as fish extractants were also investigated. The fish species used were monkfish (Lophius piscatorius), skate (Raia clavata) and cod (Gadus morrhua). It was found that 1 M NaOH was the optimal concentration for volatile base release and that 200 g l⁻¹ formaldehyde was adequate for non-TMA base sequestration. Use of PCA and TCA as fish extractants appeared to have no significant effect on TMA-N and TVB-N determinations. © 1999 Society of Chemical Industry     

The Current State of Knowledge about Essential Oil Fumigation for Quality of Crops during Postharvest

Prolonging crops’ shelf-life while retaining their high quality is a major issue related to postharvest management. During storage, fruits and vegetables are exposed to microbial attacks, which may cause spoilage. Crop deterioration causes the loss of physical properties and drops in quality and nutritional value. Hence, new techniques to improve the resistance of food products are being explored. One promising technique is fumigation. Essential oils and their constituents, due to their antimicrobial properties, are likely to be used as fumigants, as they are highly volatile, effective in low concentrations, biodegradable, and safe. Papers indicate that some of them can improve their quality by increasing the content of antioxidants. This comprehensive review aims to present the current state of knowledge about the influence of essential oil fumigation on crop quality. It covers antioxidant capacity, the content of some bioactive compounds, physicochemical properties, decay properties, and sensory attributes of fruits and vegetables treated with essential oil vapors. The review indicates that this technique might be an interesting field for further exploration due to the promising results presented in the studies. Moreover, the review presents major objectives for current studies and indicates a lack of recent papers in this field.     

不同贮藏温度下鲜湿米线的品质变化动力学模型及其货架期预测

为了研究贮藏过程中,鲜湿米线品质变化与贮藏时间的相关性,本文测定了4、10、20、25、37℃下贮藏的鲜湿米线的酸度、碘蓝值、pH值和吸水率随贮藏时间的变化,并建立了碘蓝值、pH值和吸水率的动力学模型,及以碘蓝值为终点的货架期预测模型。结果表明,鲜湿米线的碘蓝值和pH值可以建立一级动力学模型,吸水率可以建立零级动力学模型。且建立的三个模型的拟合系数R2分别为:0.9901(碘蓝值),0.9524(pH值)和0.9785(吸水率),并且其平均相对误差W分别为7.0%,5.8%和5.6%,均小于10%。以贮藏期间鲜湿米线碘蓝值的变化建立货架期模型,且货架期达终点时,碘蓝值为1.2389,其平均相对误差W为1.06%,小于10%。说明本文以碘蓝值作为终点时建立的货架期模型可以较好预测鲜湿米线的货架期。     

电子束辐照对留胚米理化性质及食用品质的影响

为了减缓留胚米储藏期间的脂肪酸败，延长留胚米的储藏期限，作者利用电子束辐照处理留胚米，并考察了储藏过程中留胚米的品质变化。结果表明，经0.5 kGy电子束辐照处理后，留胚米的留胚率、碎米率以及腰爆率变化不大，脂肪酶活性下降了28.17%，当辐照剂量增至1.0 kGy后，留胚米的腰爆率显著上升；在储藏过程中，电子束处理的留胚米样品，其水分含量下降较快，而脂肪酸值增幅速率变缓；此外，未处理样品的脂肪酶活性在储藏过程中呈现出先上升后下降的趋势，而电子束处理样品的脂肪酶活性呈线性降低的趋势；25 ℃和37 ℃储藏条件下，未处理样品的保质期均为15 d，电子束辐照处理能显著延长保质期（≥60 d）；在食用品质方面，0.5 kGy处理的样品在25 ℃储藏120 d后，其综合评分为69.9，接近相应的未处理样品（70.6），但提高辐照剂量和储藏温度均会加速留胚米的食用品质劣化。综上，电子束辐照处理是一种有效延长留胚米储藏期限的方法。     

煮制干葵瓜子品质变化及预包装产品保质期分析

以预包装焦糖味煮制干葵瓜子为实验对象，采用食品储存期动力学加速实验方法（accelerated shelf life testing，ASLT）分析添加或未添加脱氧剂的预包装样品，在40 ℃及50 ℃条件下的酸价、过氧化值及感官指标变化趋势，建立了贮存期预测动力学模型，预测了产品货架期，并评价了产品感官与酸价及过氧化值指标的联系。结果表明：随着贮存时间延长，添加或不添加脱氧剂的煮制干葵瓜子产品在40 ℃及50 ℃条件下，酸价均呈现显著上升趋势，过氧化值呈现不一致的波动式上升趋势；通过拟合回归分析并构建的煮制干葵瓜子贮藏动力学模型可得出，添加脱氧剂的预包装煮制干葵瓜子产品理论保质期可达352 d，未添加脱氧剂同类产品理论保质期176 d；此外，酸价指标对瓜子感官影响更为敏锐，而过氧化值突变趋势与瓜子贮存后期产品感官劣变程度更为一致。