Comparison of the microflora isolated from spoiled cold-smoked salmon from three smokehouses

The microflora on spoiled, sliced and vacuum packed, cold-smoked salmon from three smokehouses was quantified and characterized in two independent experiments. Large variations in the microflora were observed both within (i.e. among vacuum packs from the same batch) and among the smokehouses. Lactic acid bacteria dominated the microflora, which reached 10⁷ cfu g⁻¹. Total viable counts of microorganisms alone were not related to quality, though spoilage characteristics were typical for microbiological spoilage. Among the lactic acid bacteria, Lactobacillus curvatus (ca 52–55%) was the most common species in both experiments with Lactobacillus saké, Lactobacillus plantarum, Carnobacterium spp. and Leuconostoc spp. present in smaller numbers. In some cases, large numbers of Enterobacteriaceae were also present and identified species were Serratia liquefaciens, Enterobacter agglomerans and Hafnia alvei. The microflora on cold-smoked salmon appeared to be related to the source of contamination i.e. the raw material and/or the smokehouse rather than being specific for the product, thus rendering the identification of the specific spoilage organisms difficult.     

Pecan Texture as Affected by Freezing Rates, Storage Temperature, and Thawing Rates

Pecan texture was measured by texture profile analysis (TPA) at 80% compression before and after being frozen at 6 controlled rates, to 3 minimum temperatures and thawed at 2 rates. Freezing and thawing rates had more influence than storage temperature on pecan texture. Certain TPA parameters (i.e., hardness, area 1, fracturability and slope of linear segment of force vs. deformation curve) were more affected than others by freezing and thawing rates. Freezing and thawing at high rates had the least effect on pecan texture.     

不同冻结方式对牡蛎品质的影响

本文以冻结曲线、冻结速率、持水性、蛋白质变性程度、色差和质构为指标,研究不同冻结方式(浸渍冻结、鼓风冻结和静置冻结)对牡蛎品质的影响。结果表明:浸渍冻结组冻结速率为6.67 cm/h,分别是鼓风冻结组的5倍,静置冻结组的23倍,且其样品解冻汁液流失率和蒸煮损失最低,分别为6.75%±1.12%、42.08%±3.72%,蛋白变性程度最小,其中盐溶性蛋白含量为(48.15±5.53) mg/g,Ca²⁺-ATPase酶活为(0.202±0.020) μmol Pi/(mg·h)。浸渍冻结处理的牡蛎的弹性为(3.96±0.25) mm,与鼓风冻结组和静置冻结组比较差异显著(p<0.05)。在不同冻结方式下的色差值(L^*、a^*、b^*)、总色差(ΔE)、硬度和咀嚼性差异性不显著(p>0.05)。浸渍冻结处理牡蛎的所有品质指标都与鲜样差异不显著(p>0.05),但鼓风冻结和静置冻结在盐溶性蛋白含量、Ca²⁺-ATPase活性和弹性指标上都与鲜样差异性显著(p<0.05)。综上,浸渍冻结对牡蛎品质的保持比鼓风冻结和静置冻结更具优势,且其处理的样品品质更接近鲜样。     

超高压协同冷冻脱壳对南美白对虾品质的影响

本文以传统冷冻处理(FT)为对照,研究超高压协同冷冻处理(FT+200、300、400 MPa,1、3、5 min)对南美白对虾脱壳(脱壳时间、虾仁完整率及得肉率)及其品质(汁液流失率、持水性、pH、色泽和质构参数)的影响。结果表明:超高压协同冷冻处理有利于南美白对虾的脱壳,FT+300 MPa,1 min条件下脱壳时间较未处理、FT组分别缩短59.80%、13.54%,得肉率分别提高30.92%、7.25%,虾仁完整率明显提高。超高压协同处理后,由冷冻引起的汁液流失率显著降低,持水性显著提高,与未处理组鲜虾无显著差异;虾仁内部亮度L*、白度和总色差显著升高,压力≥300 MPa、保压时间≥3 min条件下虾仁呈现熟化现象;随着压力增加,虾仁硬度、咀嚼性增加,弹性下降。综合脱壳效果及其品质特性指标,FT+300 MPa,1 min处理可在显著提高脱壳效果的同时保持虾仁的良好品质,是一种较为理想的辅助脱壳手段。     

谷氨酰胺转氨酶对鸭胸肉糜凝胶性能的影响

以鸭胸肉糜为研究对象,探讨不同谷氨酰胺转氨酶（transglutaminase,TG）添加量（0（T1）、2（T2）、4（T3）、6（T4）、8 g（T5））对肉糜保水性、色差、质构和水分分布状态的影响。结果表明：添加TG酶显著提高鸭胸肉糜的亮度值（L*）、蒸煮得率和质构参数（P＜0.05）,降低红度值（a*）和黄度值（b*）;鸭胸肉糜的L*、蒸煮得率和质构特性随着TG酶添加量的增加而显著提高（P＜0.05）,但T4和T5组差异不显著（P＞0.05）;鸭胸肉糜的T21和T22起始弛豫时间随着TG酶添加量的增加显著缩短（P＜0.05）,T21的峰面积比例显著增加,T22的峰面积比例显著降低（P＜0.05）,表明水分的流动性降低,但T4和T5组差异不显著（P＞0.05）。综上所述,711.6 g鸭胸肉糜中添加6 g TG酶时保水性和质构最佳。     

Magnetic Resonance Imaging of Strawberry (Fragaria vesca) Slices During Osmotic Dehydration and Air Drying

The aim of this study was to develop experience in acquiring water mobility and moisture data that could be used to develop improved models for predicting water loss during osmotic dehydration and/or air-drying. One-dimensional magnetic resonance imaging protocols were used to follow temporal and spatial changes in water mobility via T₂ profiles, water content via M₀ profiles, and structural shrinkage of strawberry slices during osmotic dehydration with 600 g/kg aqueous sucrose over 2 h. Those measurements were also made for 1 h during air-drying of normal and osmotically dried slices at 20, 30, 45 and 60 °C. Air-drying above 20 °C resulted in changes in the strawberry matrix, which suggests the need for a model that incorporates the interaction between the strawberry tissue and the water that diffuses during drying. Modelling of the air-drying of osmotically pretreated slices would be complicated by the variable amounts of sucrose solution remaining after osmotic dehydration.     

High-Pressure-Freezing Effects on Textural Quality of Carrots

Raw or 3 min blanched carrots were pressurized for 45 min at ?18°C ～–20°C and then thawed at 20°C. When carrots were frozen at 100Mpa (ice I), firmness decreased and strain increased. Textural values of carrots pressurized at 200MPa (liquid), 340MPa (ice III), 400MPa (ice V) at ca. –20°C were acceptable. When pressure was increased above 500MPa, the strain increased. Release of pectin and histological damage in carrots pressurized at 200, 340 and 400MPa were less than carrots frozen at 100 and 700MPa (ice VI). After pressurization at 200 and 340MPa at —20°C, carrots were stored in a freezer (–30°C). Firmness decreased and strain increased, but textural values were higher and histological structure were more intact than those frozen at –30°C (0.1MPa) then stored. Thus, high-pressure-freezing at 200, 340 and 400MPa appeared to be effective in improving both the texture and histological structure of frozen carrots.     

Blanching, Freezing and Frozen Storage Influence Texture of White Asparagus

We studied effects of three methods of blanching in conjunction with freezing, on texture of white asparagus as defined by three measures: maximum shear force, cutting energy, and total fiber content. We also assessed shelf life of asparagus kept in frozen storage at -22°C. Methods of blanching were total immersion in hot water, progressive immersion in hot water and steam. An increase in total fiber content was found throughout frozen storage. This increase correlated with lignification of vascular bundles in the basal segment of spears, even during frozen storage. This was reflected in an increase in maximum shear force and cutting energy required. The shelf life of frozen asparagus was 12 mo using total fiber content as a criterion.     

冷藏条件下包装处理对黄冠梨品质的影响

为探究浸渍冷冻对水果质地的影响,以皇冠梨为试材,采用不同浸渍冻结温度（−20、−40 ℃）及浸渍液（单一30%氯化钙浸渍液、30%氯化钙+4%海藻糖+0.05%聚赖氨酸复合浸渍液）进行冷冻处理,通过硬度、果胶含量和组织细胞微观结构等,分析浸渍冷冻对梨质地特性的影响。结果表明：海藻糖和聚赖氨酸复合浸渍液在−40 ℃冻结组,能够更好地控制果胶损失及原果胶分解（P<0.05）,−40 ℃复合浸渍液处理组比−20 ℃单一浸渍液组水溶性果胶含量降低了31.85%,保持梨的硬度,并减少浸渍液中溶质的渗透量。傅里叶红外光谱及原子力显微结果表明,浸渍冻结处理对梨果实水溶性果胶变化有一定的影响。经过复合浸渍液在−40 ℃冻结后,梨细胞纹理清晰,排列较为规律,更接近鲜果细胞结构。可见,降低冻结温度并使用冷冻保护液可以更好地保持冷冻食品质地,降低冷冻对食品组织细胞的损伤,并抑制浸渍液溶质的大量迁移,从而提高了冷冻水果的品质。

     

Frozen Carrots Texture and Pectic Compotients as Affected by Low-Temperature-Blanching and Quick Freezing

Carrots preheated for 2 hr at 60°C and then cooked became firmer than raw or cooked carrots. After preheating, the amount of high methoxyl pectin decreased, and low methoxyl pectin increased. Firmness of carrots decreased through freezing then thawing, but preheated carrots retained firmer texture than those blanched in boiling water. Quick-freezing resulted in better texture than slow-freezing. Loss in texture was accompanied by release of pectin. Slow-freezing accelerated release of pectin as compared to quick-freezing. Preheated carrots were slower in release of pectin. The degree of esterification of pectin substances in raw carrots decreased during preheating, freezing and thawing. Cell damage in quick frozen carrots was slight. Optimum preheating occurred with 30 min at 60°C or 5 min at 70°C. Preheating and then quick freezing were effective in improving texture of frozen carrots.