前处理方式对蓝莓贮藏品质的影响

对比分析了低剂量~(60)Co γ射线辐照、二氧化氯(ClO_2)溶液浸泡、臭氧(O_3)处理及预温处理对芭尔德温蓝莓采后贮藏品质的影响。通过检测蓝莓的好果率、失重率、可溶性固形物(SSC)、多酚氧化酶(PPO)活性等指标,判断不同处理方式的贮藏效果。结果表明:4种前处理方式均能不同程度地提高蓝莓果实的贮藏品质。其中辐照处理组贮藏效果最好,能够较长时间维持蓝莓果实的好果率及最低的失重率、维持较高SSC含量,显著抑制PPO活性;而臭氧处理可维持较低的失重率,保持良好的果皮颜色;二氧化氯处理虽能提高蓝莓果实的好果率、降低蓝莓失重率,但作用效果弱于辐照组和臭氧组;预温处理虽能维持较高蓝莓果皮颜色,但导致果实失重率升高,在4种处理中贮藏效果相对较差。因此,相对其它3种贮藏方式,~(60)Co γ射线辐照预处理更能使芭尔德温蓝莓维持较好的贮藏品质,显著延长蓝莓贮藏期。     

Effects of freezing rates on starch retrogradation and textural properties of cooked rice during storage

The effects of freezing rates and storage temperatures on starch retrogradation and textural properties of cooked rice were evaluated. Cooked rice was frozen with different freezing rates and then stored at 4 °C for 14 days or −18 °C for up to 7 months. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by a differential scanning calorimetry, and textural properties were determined by a texture analyser. The results showed that the ΔH_r and hardness values had a negative correlation with freezing rate, however, a positive correlation was found between adhesiveness and freezing rate. On the other hand, the advantages (lower hardness and higher adhesiveness, less starch retrogradaton) of cooked rice gained by rapid freezing, were lost quickly in the first 3 days of storage at 4 °C. However, rapid freezing combined with −18 °C frozen storage can effectively retard starch retrogradation and maintain the textural properties of cooked rice for at least 7 months. Therefore, high quality cooked rice can be produced by combined rapid freezing with frozen storage.     

Effect of temperature, pressure and calcium soaking pre-treatments and pressure shift freezing on the texture and texture evolution of frozen green bell peppers (Capsicum annuum)

The firmness of green bell pepper (Capsicum annuum) was studied under different processing conditions. Thermal texture degradation kinetics of pepper tissue between 75 and 95 °C could be accurately described by a fractional conversion model. The firmness of pre-processed pepper increased when the samples were submitted to several heat, pressure, and combinations of heat/pressure and calcium soaking pre-treatments. Pre-heating at 55 °C during 60 min and mild heat/high-pressure treatments (200 MPa at 25 °C, 15 min) yielded the best results, which were further improved when combined with calcium soaking. These pre-treatments significantly slowed down thermal texture degradation of pepper at 90 °C, a typical temperature used for pepper blanching prior to freezing. The above-mentioned pre-treated samples showed a significant reduction in firmness when frozen by regular freezing at 0.1 MPa. The same samples showed no changes in firmness when frozen by high-pressure shift freezing at 200 MPa. When freezing was carried out by high-pressure shift and after frozen storage (−18 °C) for 2.5 months, pressure pre-treated pepper showed a better retention of texture than thermal pre-treated pepper.     

Non-enzymatic browning and estimated acrylamide in roots,tubers and plantain products

Acrylamide has been discovered in foods, especially high carbohydrate foods that are dry-cooked (baked, fried or roasted) at high temperatures which also create the conditions for non-enzymatic browning. Baking, frying and roasting are common food preparation methods in Ghana. Fifteen different high carbohydrate foods in Ghana, that undergo dry-cooking, have been investigated for non-enzymatic browning and acrylamide production. The products that showed notable non-enzymatic browning and acrylamide levels include fried sweet potato, plantain chips from the fresh produce, with their respective non-enzymatic browning and acrylamide values as 0.095 ± 0.006 optical density (OD), 1043 ± 47.6 parts per billion (ppb); 0.034 ± 0.03 OD, 568 ± 22.9 ppb. Roots and tuber products had relatively high non-enzymatic browning and acrylamide levels while plantain products showed low levels of non-enzymatic browning and acrylamide.     

Effects of pre-treatments on the shrinkage and textural properties of fried sweet potatoes

This work studied the effects of various pre-treatments (blanching, freezing, air drying, osmotic dehydration and control) on the shrinkage and textural properties of fried sweet potatoes. Sweet potato discs were pre-treated and fried in pure canola oil at 170 °C for 0.5-5 min. Bulk density of the fried samples decreased while porosity increased with frying time. Effect of pre-treatment though not significant on bulk density but was significant (P<0.05) on product porosity. Control samples exhibited less shrinkage than pre-treated samples. Maximum change in diameter of samples ranged between 6.7% and 10.2% depending on pre-treatment. Maximum change in sample thickness was observed by 120 s of frying and the highest value was 18.3%. Pre-treated samples had higher difference in thickness compared to the control samples. Change in sample volume increased with frying time reaching a maximum at 120 s after which it either decreased or levelled off. Generally, pre-treatment improved the textural properties of fried samples in product hardness, springiness, chewiness, cohesiveness and adhesiveness.     

Effects of pressure-shift freezing and conventional freezing on model food gels

Summary Gels of agar, starch, ovalbumin, gelatin and an industrial β-lactoglobulin protein isolate, were frozen conventionally in a −30 °C freezer and by pressure-shift freezing at 200 MPa at −15 °C. Thawing was carried out conventionally at 20 °C and by the application of a pressure of 200 MPa. The microscopic structure and mechanical properties of the thawed gels were compared with those of the initial gels. Microscopic examination showed that pressure-shift freezing produces smaller and more uniform ice crystal damage than conventional freezing at −30 °C. The results also suggest that the freeze-thaw behaviour of food gels can be categorized into two general types: (1) gels which have a reduced gel strength as a result of mechanical damage to the gel microstructure caused by ice crystal formation, and (2) gels which have an enhanced gel strength, as a result of molecular structural changes that take place in the frozen state. Agar and gelatin were found to be typical of type (1) gels, whereas starch, β-lactoglobulin protein isolate and ovalbumin were found to be typical of type (2) gels. In the case of starch, retrogradation during thawing was found to be the most important factor.     

车前草桃果复合饮料的研制

以车前草、桃子为主要原料得色、香、味、品质俱佳的新型营养饮品，试验对其加工过程中的取汁方法，酸味剂、稳定剂的选择，产品配方等主要工艺进行了研究。     

Kinetics of moisture loss and fat absorption during frying for different varieties of plantain

This study compares the behaviour of four varieties of green plantain at their initial stage of maturity during the frying process. A variety traditionally used for the manufacture of thin plantain chips (Dominico Hartón commun) and three other varieties found in Latin America (Bouroukou, Bluggoe and FHIA 21) were used. The varieties were characterised by measuring initial moisture content, total sugar content, reducing sugar content, starch content and apparent density. Moisture loss and fat uptake kinetics during frying were assessed at different temperatures (145, 165 and 185°C). With all four varieties, the time required to produce a final moisture content of 40 g kg⁻¹ (wb) was about 90 s at 165°C and 185°C. Use of a lower temperature (145°C) extended the processing time to 150 s. On the other hand, temperature had very little effect on fat content, which proved to be essentially determined by the variety of plantain. Fat content for final water content levels of 40 g kg⁻¹ (wb) ranged from 300 g kg⁻¹ (wb) for Bouroukou to 450 g kg⁻¹ (wb) for Bluggoe regardless of the processing temperature. © 1999 Society of Chemical Industry     

冻结速率对鸡汤理化及流变特性的影响

以新鲜鸡汤为对照,探究不同冻结速率(-20、-40、-80℃冻结)对鸡汤理化性质和流变特性的影响。结果表明,-20℃鸡汤冻结组属于慢速冻结,-40、-80℃鸡汤冻结组属于快速冻结。冻结处理会使pH、可溶性蛋白含量降低,电导率、L*值增加。慢冻组的电导率、硫代巴比妥酸值(thiobarbituric acid reactive substances,TBARS)可溶性蛋白和速冻组的pH、可溶性蛋白均与新鲜鸡汤差异显著(p0.05)。慢冻组与速冻组的电导率、TBARS差异显著(p0.05)。速冻组-40℃和-80℃的鸡汤除了电导率,其他理化指标均无显著差异(p0.05)。随剪切速率增加,鸡汤黏度值减小,剪切应力增大。剪切速率相同时,冻结组鸡汤表观黏度和剪切应力均低于对照组,-20℃慢速冻结对鸡汤流变影响较显著。速冻比慢冻对鸡汤溶液黏度、剪切力影响较小。综合分析,快速冻结更适合鸡汤冷冻处理。     

浅谈白条肉在冷却和冻结过程中的干耗

目前在猪肉的冷加工过程中,一般冷却肉的加工温度为0～15℃,冷冻肉的加工温度为-40～-15℃.肉类在冷加工过程中,由于表面层的水分蒸发,使肉类不断减重,这种减重的现象,称为"脱水",俗称"干耗".     

不同预处理方式对超临界流体萃取葡萄皮精油影响的研究

针对葡萄皮渣综合利用问题,研究了超临界流体萃取技 术提取葡萄皮精油过程中不同预处理方式对萃取率的影 响。结果表明,不同含水量条件下,粉碎粒度由0.9mm降 低到0.2mm,萃取率均有明显提高;含水量越低萃取率越 高,含水量7.26％时的萃取率相应低于含水量5.53％的处 理组;葡萄皮的真空冷冻干燥预处理方式最适于超临界 流体萃取葡萄皮精油,萜烯类化合物得率为78.16％。      

冻结速率对冻鸭品质特性的影响

鲜鸭分别于-35℃浸渍冷冻液和风冷冷库中冻至-18℃,然后在-18℃保藏库中贮藏5个月,以解冻汁液流失、蒸煮损失、肌肉剪切力、色泽、pH、TVB-N和微生物为指标,研究冻结速率不同对鸭在冷冻和贮藏过程中品质变化的影响,采用回归分析预测其贮藏期。结果表明:鸭体中心温度降到-18℃,浸渍式冷冻处理组用时仅仅52min,显著短于风冷组的738min;除pH值无显著差异外,浸渍式冷冻组的其他各项品质指标显著优于风冷冷冻组。     

Effects of maturity and drying method on the physico-chemical and reconstitution properties of plantain flour

Effects of maturity and drying method on physical, physico-chemical and reconstitution properties of plantain flour were investigated. Colour ( L*a*b* ) parameters of dried flours were measured, and the delta chroma (Δ C ) and colour difference (Δ E ) were calculated. Particle size, physico-chemical (pasting) using Rapid Visco-Analyser and reconstitution properties of dried plantain flour were determined. Colour parameters of foam-mat [ L* (57.56–66.33), a* (5.29–6.77), b* (11.82–13.33)], sun [ L* (60.18–67.45), a* (5.43–5.88), b* (13.19–13.25)] and oven [ L* (58.78–66.44), a* (6.08–6.33), b* (11.96–12.78)] dried flours were significantly different ( P  < 0.05). Generally, more than 40% of the flours were retained by the 710 μm sieve. Generally, peak (–2.08–166.00), breakdown (1.25–29.42), final (–1.00–298.67) and setback (1.50–156.92) viscosities varied with drying method and maturity. Peak time and pasting temperature varied from 5.20–6.87 s and 92.30–94.55 ^°C, respectively. pH (4.26–4.97), titratable acidity (0.10–0.50% citric acid), soluble solids (3.25–30.76), moisture (8.77–65.99%) and dry matter (34.01–91.23%) contents were significantly ( P  < 0.05) affected by maturity and drying method.     

Effects of raw materials,processing conditions and packaging on the quality of plantain chips

The effects of raw material, processing conditions and packaging on the quality of plantain chips were investigated. Two cultivars of plantain Musa spp—Agbagba and Obino lewai—as well as cooking banana were used for the study. The fruits were at stages 1 to 4 of the banana ripening chart. The study started with a consumer survey aimed at product definition. This was followed by series of experiments to determine the effects of raw material, processing conditions and packaging on the quality of plantain chips. A correlation analysis was also carried out on the physical and chemical characteristics of raw plantain. The work revealed that the stage of ripeness of raw material had some effect on the quality of chips as there was gradual increase in pulp/peel ratio and sugar was significantly different (P < 0·05). Moisture content of pulp/texture of pulp, texture of pulp/sugar content of pulp and texture of pulp/ripening stages were negatively correlated, while pulp/peel ratio and moisture content of pulp were positively correlated. Chips packed in 80 μm high-density polyethylene pouches and stored at various relative humidities had extended shelf-life compared with the low-density polyethylene packed chips stored at the same relative humidities. This was due to the inadequacy of the low-density polyethylene in giving the required protection against moisture transmission thereby resulting in soggy chips in shorter periods. The implication of the findings on the formulation of a guideline for the processing of a good-quality plantain chips for the marketing system is discussed.     

新型冷冻和解冻技术在肉类食品中的应用研究进展

冻藏是肉类食品的主要贮藏方式之一,而冷冻和解冻过程是影响冻藏食品品质的重要因素。传统的冷冻和解冻方法耗时长,极易导致营养成分的流失及品质的降低,已不能满足现代食品工业的发展需求。因此,发展能够较好地保持肉类食品品质的新型快速技术具有重要的意义。文中对目前先进的冷冻和解冻技术在肉类食品中的应用研究进行重点综述,分析了各技术现阶段存在的不足和未来的研究趋势,为肉类食品冷冻工业的实际生产提供相关指导。