Storage Quality of Fresh and Frozen-thawed Fish in Ice

The objective was to determine whether traditional quality indexes of fresh (unfrozen) fish like sensory analysis, bacterial counts and trimethylamine content could be applied to thawed whole cod, cod fillets and ocean perch fillets kept in ice. Freezing and short-term freezer storage (≤5 wk at ?25°C) had very little effect on bacterial counts. During long-term freezer storage (≥14 wk at ?25°C) total counts were reduced as well as counts of trimethylamine oxide-reducing bacteria in cod fillets but not in ocean perch fillets. When the thawed fish was unacceptable the trimethylamine was <1 mgN/100g. Trimethylamine as a spoilage indicator was of no value when evaluating spoilage of thawed whole cod, cod fillets and ocean perch fillets kept in ice.     

Differentiation of Frozen and Unfrozen Beef Using Near-Infrared Spectroscopy

Freezing and thawing affects the quality of meat. The present paper focuses on using near-infrared (NIR) diffuse reflectance spectroscopy to detect whether beef has been frozen and thawed. Intact beef and drip or centrifuged meat juice of M longissimus dorsi slices from 40 cattle were used as samples. The meat juices were analysed using dry extract spectroscopy by infrared reflection (DESIR). From centrifuged juice 80 samples were classified 100% correctly, using crossvalidation, into frozen or unfrozen beef by the K nearest neighbours method. This was obtained by high-order principal components from 400–2500 nm spectra. Other multivariate techniques, smaller wavelength ranges and detecting refrozen, thawed beef also gave results between 90 and 100%. Analyses of drip loss, exudative properties, water-holding capacity and dry matter of meat juice supported the interpretation of the NIR measurements. The results showed that NIR might be used as a screening method to differentiate unfrozen and frozen beef. © 1997 SCI.     

Study on the electric conduction properties of fresh and frozen–thawed grass carp (Ctenopharyngodon idellus) and tilapia(Oreochromis niloticus)

Electric conduction properties of fresh and frozen–thawed grass carp (Ctenopharyngodon idellus) and tilapia (Oreochromis niloticus) were studied by measuring their impedances under different frequencies. The impedances varied as frequency changed. Although impedances of both fresh and frozen–thawed fish decreased as frequency increased from 1 to 20 kHz, change ratio of impedance (Q value) of fresh fish was evidently higher than that of frozen–thawed fish. The Q values of fresh grass carp and tilapia on the 1st, 3rd, 6th, 8th, 10th days were 60.53%, 52.24%, 35.47%, 26.86%, 21.17% and 73.13%, 52.70%, 41.06%, 39.28%, 36.31%, while frozen–thawed grass carp and tilapia were 9.65%, 11.21%, 9.58%, 8.89%, 9.13% and 18.26%, 12.80%, 13.46%, 12.16%, 12.91%, respectively. Electric conduction is a rapid, easy to use, portable and cost‐effective method for in situ analysis at practical level. Therefore, it is feasible to identify fresh and frozen–thawed fish according to the change ratio of their impedances.     

Freshness Assessment of Thawed and Chilled Cod Fillets Packed in Modified Atmosphere Using Near-infrared Spectroscopy

Near-infrared reflectance (NIR) spectra was recorded of 105 samples of cod mince prepared from chill stored thawed cod fillets of varying quality in modified atmosphere packaging (MAP). Traditional chemical, physical, microbiological and sensory quality methods developed for assessing fresh fish products were determined on the same cod fillets. The purpose was to evaluate the potential of NIR spectroscopy for estimating (i) frozen storage temperature, (ii) frozen storage period and (iii) chill storage period of thawed-chilled MAP Barents Sea cod fillets. Furthermore, the potential for measuring of selected quality attributes as drip loss, water holding capacity and content of dimethylamine by NIR was evaluated. The results of the investigation were presented using multivariate modelling methods such as partial least-squares regression (PLSR) and discriminant partial least-squares regression (DPLSR). Systematic differences in the NIR measurements on minced cod fillets were primarily due to the chill storage duration (days at 2°C) on thawed-chilled MAP fillets. PLSR models based on wavelengths selected by a new Jack-knife method resulted in a correlation coefficient of 0.90 between measured and predicted duration of chill storage period (days at 2°C). The root-mean-square error of cross-validation (RMSECV) was 3.4 d at 2°C. NIR measurements provided promising results for evaluation of freshness for thawed-chilled MAP cod fillets completing the traditionally quality methods. However, it is necessary to study the effect of e.g. sample preparation, season, fishing ground and cod size together with more sophisticated pre-treatments of NIR spectra before the NIR method can be integrated as a method for evaluation of thawed-chilled MAP cod fillets.     

Near-Infrared Spectroscopy for Classification of Oranges and Prediction of the Sugar Content

A nondestructive method for the classification of orange samples according to their growing conditions and geographic areas was developed using Vis/Near infrared spectroscopy. The results showed that the NIR spectra of the samples were moderately clustered in the principle component space and pattern recognition wavelet transform (WT) combined artificial neural network (BP-ANN) provided satisfactory classification results. Additionally, a partial least square (PLS) method was constructed to predict the sugar content of certain oranges. It showed excellent predictions of the sugar content of oranges, with standard error of prediction (SEP) values of 0.290 and 0.301 for Shatangju and Huangyanbendizao, respectively.     

鲜食玉米冷冻加工过程节能技术分析

鲜食玉米由于其良好的保健功效,越来越受到人们的喜爱,具有广阔的市场前景.作为鲜食玉米保鲜重要环节的冷冻加工过程,其能耗问题严重影响了鲜食玉米的经济效益.本文就鲜食玉米的冷冻加工过程进行了分析,提出了鲜食玉米保鲜过程中的节能措施.     

两种鲜豆荚的速冻保鲜

介绍了两种速冻鲜豆荚的生产工艺，将新剪豆荚及时浸泡于2％～3％的氯化钠水溶液中。以防切口褐变。热烫的适宜温度为96～98℃，时间：青豌豆荚为1．0～1．5min；青刀豆荚为1．0～2．0min，以抑制氧化酶活性。采用单体快速冻结能有效避免慢冻时产生大量冰晶，以防豆荚爆裂，冻结温度为-20～-25℃。时间为8～10min，温度过低会引起豆荚断条。     

基于偏最小二乘法的板栗近红外光谱分析模型的建立

目的:应用近红外光谱技术和化学计量学方法,建立板栗品质分析的近红外光谱模型。方法:采用傅里叶变换近红外光谱仪,采集样品的近红外漫反射光谱,再用传统理化分析方法测得样品的各项品质参数,采用偏最小二乘法(PLS)建立定标模型,内部交叉验证法对模型进行检验。结果:对板栗分别建立了水分、淀粉、硬度和糖度的PLS模型,4种PLS模型都非常理想,模型的相关系数均大于0.99。结论:采用近红外光谱法可以实现板栗品质指标的快速无损检测。     

近红外定量分析青烟叶中K、Ca、Mg含量的研究

本文利用近红外光谱仪(NIR)结合偏最小二乘法,用漫反射方法测定了青烟叶中K、Ca、Mg三种化学成分,试验证明,NIR可以用于测试青烟叶中这三种化学成分的含量。      

近红外光谱分析技术快速测定儿童高钙奶粉理化指标的研究

从化学计量学角度研究了近红外光谱技术测定儿童高钙奶粉理化指标的原理。使用多元线性回归法分别建立了近红外检测的儿童高钙奶粉水分、蛋白、脂肪、乳糖和蔗糖的快速测定模型。将近红外法测定结果和标准方法测定结果进行比较,结果吻合理想。近红外光谱法具有分析快速、操作方便、节约检测成本的优点,非常适合用于奶粉生产过程中的质量控制。     

基于主成分分析与近红外光谱技术的窖泥聚类研究

采用近红外光谱技术和主成分分析法相结合的检测手段,从60年、90年、200年窖龄的窖池和封窖泥中取样,每个窖池样本为12个,测量其近红外漫反射红外光谱,在4000～10000 cm-1区间选取不同范围内的光谱数据,对48个样本进行主成分分析,作二维线性投影图和三维线性投影图,比较了48个样品在红外光谱上的差异程度,发现基于傅里叶变换近红外光谱的主成分分析投影图能够较好地表征48个样品的类别关系,不同窖龄的样本在空间分布中能够得到较好的区分。结果表明,应用近红外漫反射光谱法能够鉴别窖泥的使用年份。作为一种窖泥质量检测手段,该方法具有一定的应用价值。