Hot air dehydration of figs (Ficus carica L.): drying kinetics and quality loss

The dehydration of fruit from fig trees is normally achieved by sun drying. There is concern about the safety of the end product, mainly because there is a risk of the development of aflatoxins. These concerns can be overcome by artificial drying (oven dehydration). Fig fruits of a local cultivar, which were either pre‐treated by blanching or blanching plus sulphuring or not treated at all, underwent hot air dehydration under mild processing conditions in a pilot airflow cabinet dryer. Sampling was carried out at regular intervals to calculate the rate of dehydration and assess quality changes. Microbiological counts and nonenzymatic browning were also monitored. Pretreatments resulted in a shorter processing time, compared with control fruits. In general, a falling dehydration rate period was observed. A dramatic loss of ascorbic acid was recorded, while an informal sensorial assay of the dried fruits gave a positive assessment.     

Detection of peroxidase activity in two-dimensional gel electrophoresis

Two-dimensional gel electrophoresis is a well-known technique to detect proteins and identify them by mass spectrometry. Peroxidase activity is commonly revealed in different fields of investigation by adding a substrate to the enzyme in the sample, in the presence of hydrogen peroxide. From these two points, a useful procedure to detect this enzymatic activity on two-dimensional gels is described. The novelty and interest of this technique is that the electrophoresis developed combines a nondenaturing gel with running denaturing conditions, allowing peroxidase activity to remain after the whole process. Therefore, the isoelectric point and the molecular weight can be used to separate different isoforms of peroxidase on a two-dimensional gel.     

Effect of carbon dioxide on the inactivation of florida spiny lobster polyphenol oxidase

Florida spiny lobster (Panulirus argus) polyphenol oxidase (PPO) exposed to CO₂ (1 atm) at 33, 38, and 43°C showed a decrease in enzyme activity with increased heating time. Enzyme inactivation by CO₂ was faster for PPO heated at 43 than at 33 or 38°C. Inactivation kinetics revealed PPO was more labile to CO₂ and heat in the range 33–43°C than to heat alone. Kinetic data also revealed that CO₂, in addition to pH changes, was involved in the loss of PPO activity. Studies using get electrophoresis showed no differences in protein patterns and isoelectric point between CO₂-treated and non-treated control. The pH of CO₂-treated PPO stock solution was brought back from 5.4 to 8.0 after 6 weeks of frozen-storage and no enzyme reactivation was observed.     

防止甘薯破碎后的褐变提高淀粉白度的研究

根据甘薯破碎后的褐变机理，确定了在甘薯破碎的最初阶段加入一定量的酸式亚硫酸钠，同时在淀粉乳沉降的不同阶段控制不同的ｐＨ值，使淀粉的白度和淀粉乳的沉降速度有了明显的提高。通过测定发现其白度在同等条件下与不加酸式亚硫酸钠相比提高了４～５     

莴笋多酚氧化酶的主要特性及其酶促褐变的抑制

研究了莴笋中多酚氧化酶的酶反应进程、最适温度、最适pH值和底物浓度对酶活性的影响.通过L9(34)正交试验,筛选出以抗坏血酸、亚硫酸氢钠、氯化钙和柠檬酸为主要褐变抑制剂的最佳配方,并对化学试剂的抑制机理进行了探讨.当抑制效果最好时,各化学试剂的最佳组合为:0.5%氯化钙 0.2%柠檬酸 0.25%抗坏血酸 0.3%亚硫酸氢钠.     

甘薯淀粉提取中的安全非硫护色工艺

根据食品加工过程中酶促褐变和非酶褐变的机理,以褐变强度(BrowningDensity)为主要试验指标,在甘薯淀粉提取过程中,对常见的几种能抑制酶促褐变的安全成分如NaCl、Vc、柠檬酸等进行了实验,进而又通过正交试验得到了一种安全有效的、可以代替亚硫酸盐护色功效的复合护色液:即含NaCl2.5%、Vc 0.3%、柠檬酸 1.0 0 %、CaCl2 0.4 5%的水溶液 在加工过程中,以该种复合护色液处理破碎物料 2 0min,可以得到与传统S0 2 抑酶漂白同样好色泽的终产品     

Improvement of the commercial quality of chilled Norway lobster (Nephrops norvegicus) stored in slurry ice: Effects of a preliminary treatment with an antimelanosic agent on enzymatic browning

The use of slurry ice is gaining increasing importance as an advanced method for the hygienic and efficient chilling and sub-zero storage of aquatic food products. In this work, this technology was applied as a novel technique for the chilling and storage of Norway lobster (Nephrops norvegicus) – a crustacean species of high-commercial value – under refrigeration conditions at −1.5 °C. In addition, the effects of a preliminary treatment with 0.5% Na HSO₃ on surface browning were evaluated and compared with the results obtained in control batches not subjected to such treatment. The processing of lobster in slurry ice significantly (p < 0.05) slowed down microbial spoilage, as determined by the counts of aerobes, psychrotrophs, proteolytic bacteria, and lactose-fermenting Enterobacteriaceae, and by the formation of volatile amines. Likewise, the autolytic breakdown mechanisms – as determined by the K value – were also significantly (p < 0.05) inhibited in the slurry ice batch. Remarkably, preliminary treatment with 0.5% sodium metabisulphite permitted better maintenance of the parameters involved in sensory quality – especially as regards the aspect of the carapace – as compared with non-treated batches, and allowed a shelf life of 9 days without surpassing the 150 mg/kg legal limit established for this food additive. On contrast, the non-treated batch stored in slurry ice exhibited a shelf life of 5 days. The combination of technological treatments proposed in this work – preliminary antimelanosic treatment and storage in slurry ice – may be successfully applied to other fresh and frozen shellfish species with a view to extending shelf life and to avoiding the legal and toxicological problems derived from current abuse of such antimelanosic agents to prevent shellfish browning.     

The Effects of Antioxidants on Browning and on Degradation Products Caused by Dehydroascorbic Acid

The efficiency of L-cysteine (cysteine) and sodium sulfite as antioxidants was examined in the browning of an aqueous solution of 100 mM dehydroascorbic acid (DHA). The browning was suppressed at 100 mM cysteine and at 40 mM and higher concentrations of sodium sulfite, but it increased in the presence of 10 mM of those agents. These agents did not allow the reduction of DHA to L-ascorbic acid (AA). These results suggest that the suppression or acceleration of browning is likely to be related to some degraded intermediates of DHA. The two colorless intermediates, which during DHA breakdown eventually transform into browning pigments, were discussed with regard to the browning regulation mechanism.     

The contribution of coloured Maillard reaction products to the total colour of browned glucose/l-alanine solutions and studies on their formation

 Thermal treatment of aqueous solutions of glucose and l-alanine in the presence of furan-2-carboxaldehyde (mixture I) resulted in the formation of a variety of coloured compounds, amongst which (1R,8aR)- and (1S,8aR)-4-(2-furyl)-7-[(2-furyl)methylidene]-2hydroxy-2H,7H,8aH-pyrano[2,3-b]pyran-3-one (1a/1b) and 3,5-dihydroxy-2-[(E)-(2-furyl)methylidene]methyl-5,6-dihydropyran-4-one(2) were identified as the most intense by application of the colour dilution analysis (CDA). To study how the colorant formation is influenced by the solvent, the Maillard mixture was then heated in a water/methanol mixture (mixture II). Besides 1a/1b and 2, additional coloured compounds were detected in mixture II, amongst which (E)- and (Z)-6-hydroxymethyl-2-methoxy-4-[(2-furyl)methylene]-2H-pyran-3-one (3a/3b), (E)- and (Z)-2-methoxy-4-[(2-furyl)methylene]-2H-pyran-3-one (4a/4b) as well as (1R,8aR)- and (1S,8aR)-4-(2-furyl)-7-[(2-furyl)methylidene]-2-methoxy-2H,7H,8aH-pyrano[2,3-b]pyran-3-one (5a/5b) could be distinguished from the less colour-active by application of CDA. To measure the contribution of these colorants to the overall colour of the browned Maillard mixtures I and II, colour activity values were calculated as the ratio of the concentration to the visual detection threshold of each colorant. By application of this colour activity concept, 3.3% of the total colour of the Maillard mixture II was shown to be caused by the 2H,7H,8aH-pyrano[2,3-b]pyran-3-one chromophore (1a/1b and 5a/5b). Based on a labelling experiment with glucose-6-[¹³C₁], the formation pathway leading to this key chromophore, involving a retro-aldol cleavage of the C(6) carbon from the hexose skeleton, was clarified. Received: 7 May 1998     

固载二氧化氯对最小加工竹笋品质和生理的影响

采用固体二氧化氯处理最小加工竹笋,于4 ℃贮藏12 d。以呼吸强度、颜色、硬度、苯丙氨酸解氨酶（PAL）、多酚氧化酶（PPO）、过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）和谷胱甘肽还原酶（GR）活性、超氧阴离子自由基生成速率、总抗氧化能力和菌落总数等为指标,研究0.50 mg/L二氧化氯对最小加工竹笋品质和生理的影响。结果表明：用0.50 mg/L的二氧化氯处理,可降低最小加工竹笋呼吸强度,抑制竹笋贮藏期间硬度的上升;延缓PAL、PPO活性的增加;提高CAT、APX和GR的活性,降低超氧阴离子自由基的生成速率,提高总抗氧化能力。