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.     

Effect of initial slight oxidation on stability of polyunsaturated fatty acid/protein mixtures under controlled atmospheres

A mixture of unsaturated fatty acids (FA), mainly linolenic acid, and bovine serum albumin (BSA) was incubated under several different atmospheres to study the effect of these atmospheres on the stability of FA to oxidation. Four experiments were carried out simultaneously, which consisted of the incubation of the FA/BSA mixture under air, nitrogen, air in the presence of 200 ppm of butylated hydroxytoluene, and air for 6 h and then under nitrogen. The four experiments were tested for lipid oxidation and color changes by measuring absorbances at 234 and 270 nm, formation of thiobarbituric acid-reactive substances, and color differences and yellowness index. The samples that were oxidized with air before storage under nitrogen were the most stable against lipid peroxidation and exhibited the smallest color changes. These results suggest that a slight and controlled lipid oxidation improved the oxidative stability of FA/BSA mixtures.     

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     

应用"湿冷系统”贮藏新鲜荔枝的研究

湿冷系统能为荔枝提供低温高湿的贮藏条件,结合臭氧杀菌,较好的控制了荔枝的褐变与腐烂,为荔枝的产业化提供了一个新的思路.     

苹果汁贮存过程中非酶褐变因素及其控制

苹果汁贮存过程中影响非酶褐变的因素很多。本文研究结果为pH=4.0和低温（4.4℃或更低）时,非酶褐变程度较轻。HMF的含量可用作评估果汁的品质的指标。     

姜多酚氧化酶特性的研究

姜在加工中易发生褐变。本文采用分光光度法,研究了姜组织中多酚氧化酶(PPO)的活性,以及PPO的最适pH值,最适温度,热稳定性等特性和0.1%的亚硫酸氢钠对PPO的抑制效果。结果表明:其最适pH值范围为7.4～8.0,pH4.8以下可抑制酶活性;最适温度范围为40～60℃,在70℃以下,其热稳定性较强,大于80℃时,其热稳定性急剧下降,80～90℃热处理1～5min可使酶失活;0.1%的亚硫酸氢钠对PPO有显著抑制效果。     

板栗乳饮料的研究

对板栗乳饮料的加工技术进行了研究,确定了板栗浆防褐变、饮料稳定性等工艺条件。     

Chemical and microbial stability of high moisture dried apricots during storage

BACKGROUND: This study was conducted to determine the chemical and microbial stability of high moisture (HM) dried apricots during storage at 5, 20 and 30 °C for a period of 8 months. HM dried apricots were obtained by rehydrating dried apricots in ‘water’ and ‘water + H₂O₂’. RESULTS: Analysis of kinetic data suggested first‐order models for loss of SO₂ and non‐enzymatic browning reactions. Higher storage temperatures increased the rate of SO₂ loss and formation of brown colour in HM dried apricots. Results from extensive colour measurements (non‐enzymatic browning, reflectance colour and β‐carotene) revealed that the colour of HM dried apricots stored at 5 °C was almost unchanged during 8 months of storage. The colour of samples stored at 30 °C was unacceptable starting from 2 months of storage. Total mesophilic aerobic bacteria counts decreased 0.7, 1.1 and 1.5 log cycles after 8 months of storage at 5, 20 and 30 °C, respectively. For the same storage period, the decrease in mesophilic bacteria was 0.62 log cycle in samples rehydrated in ‘water + H₂O₂’ and stored at 20 °C. CONCLUSION: These results suggest that HM dried apricots should be stored at temperatures lower than 20 °C to preserve the characteristic golden yellow colour. A relatively low level of SO₂ (1458 mg kg^?1 at 200 g kg^?1 moisture level) was sufficient to prevent the growth of spoilage organisms in HM dried apricots at all three storage temperatures. Copyright © 2008 Society of Chemical Industry