Effect of synthetic antioxidants on storage stability of Khoa – a semi-solid concentrated milk product

Effect of synthetic antioxidants on storage stability of freshly prepared khoa was evaluated. Free fatty acids (FFA), peroxide value (POV) and iodine values (IV) were used to assess the development of rancidity during 30 days of storage of khoa at 25 and 45 °C. Butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT) were added to freshly prepared khoa to extend the storage life. After 30 days of storage at 45 °C, freshly prepared khoa containing 200 ppm of BHA and BHT showed lower values of FFA (0.066%, 0.058%) and POVs (23.0, 21.0 meq/kg) than the control samples (FFA 0.320%, POV 127 meq/kg). Iodine values of khoa sample containing 200 ppm of BHA and BHT were 67 and 69 after 30 days storage at 45 °C. However, iodine value of a khoa sample without antioxidant (control) after 30 days of storage at 45 °C was 30. Similarly, khoa samples treated with 100 ppm of BHA, along with 100 ppm of BHT, showed FFA value (19.0%), POV (0.049 meq/kg) and iodine value (72) after storage for 30 days at 45 °C. These results illustrate that synthetic antioxidants inhibited the development of rancidity during storage of khoa. Therefore, storage life of khoa can easily be extended for 30 days by the addition of BHA and BHT.     

SURVIVAL AND GROWTH OF SELECTED MICROORGANISMS IN KHOA DURING PREPARATION AND STORAGE

The survival of Escherichia coli and Staphylococcus aureus during the production of khoa, a heat concentrated Indian milk-based product, was investigated. Heat processing of milk containing from 3.6 to 6.5% fat at either 63 or 73C eliminated all E. coli. Under similar processing conditions , S. aureus was recovered, but only when heated in milk at 63C containing 6.5% fat. Potassium sorbate (3000 ppm) appeared more effective in inhibiting the growth of selected yeast and molds in khoa at 7C, compared to ascorbic acid (3000 ppm). Reducing the water activity (a _w) of khoa from 0.97 to 0.93 did not appear to enhance the preservative effect. The reduction of E. coli or S. aureus in khoa during prolonged storage at 6–7C, was less than one log cycle, regardless of a _w or preservative type. Survival of S. aureus in khoa appeared to be enhanced with a decrease in a _w. The potential for pathogens to survive in khoa during processing should be taken into consideration when formulating heating protocols.     

Microstructure and texture of khoa and gulabjamun made from cows' milk: Heat-induced changes during processing and frying

Scanning and transmission electron microscopy was carried out to study heat-induced structural changes that occur during the processing of khoa (a heat-desiccated Indian milk product) and gulabjamun (a product obtained by frying khoa, admixed with starch, in clarified butterfat and subsequently soaked in 60% sugar syrup). Constant boiling of milk during khoa manufacture led to the formation of casein-whey protein complexes, which coalesced gradually on the progress of boiling, forming a fuzzy-agglomerated mass and finally precipitated as heat-induced milk gels, joined together by thick protein bridges. Further heat desiccation of this gel resulted in the compaction of the protein agglomerates with reduction in void spaces and fat globules interspersed in between (ie khoa). Frying of khoa in clarified butterfat resulted in the enlargement of the voids, producing a loose matrix having starch particles interlinked loosely with the agglomerated protein bodies and the clumped fat globules cemented in it (ie gulabjamun). The laboratory and market gulabjamun had significant structural similarities in the fat and protein moieties but differed markedly in the textural values, probably due to the differences in the chemical composition and typical structural manifestations of the starchy materials in the market gulabjamun. Composition and texture can be explained by the microstructural attributes for both khoa and gulabjamun.     

Effect of preparation and storage of khoa on physicochemical properties of milk fat

The changes in milk fat during the preparation and storage of khoa were studied in three different seasons. Milk fat was extracted from the samples with chloroform using Soxhlet extraction. The solvent was evaporated using a vacuum evaporator followed by nitrogen flushing. The extracted fat samples were analysed for Reichert–Meissl, Polenske, saponification and iodine values, butyro‐refractometer reading at 40 °C and free fatty acids (FFAs). The study revealed an increase in the FFA content during conversion and storage of khoa, while there were small changes in other physicochemical properties of milk fat during the preparation of khoa from raw milk and its subsequent storage at room temperature.     

Characterisation and comparison of khoa prepared from camel milk with that from cow and buffalo milk

Khoa, a heat‐concentrated milk product, is used as a base material for the manufacture of many popular sweets. The comparison was made between various chemical compositions and characteristics of the khoa prepared from the camel milk with that prepared from the cow and the buffalo milk samples. The khoa prepared from the camel milk had the higher moisture, ash, acidity, soluble nitrogen, free fatty acids and peroxide value, but lower in fat, protein and lactose contents than that prepared from the cow and buffalo milk samples. There was no significant (P > 0.05) difference in 5‐hydroxymethyl furfural between khoa samples prepared from the three milks.     

Vitamin C kinetic degradation of strawberry juice stored under non-isothermal conditions

Strawberries are a good source of nutritional compounds and may be considered among the fruit most rich in ascorbic acid (AA). Strawberry juice is easily damaged in transit due to temperature fluctuations that may significantly reduce shelf life. In this way, the use of “best before” and “use by” dates should be reconsidered in the light of temperature variability during transport or storage. Kinetic degradation of ascorbic acid and shelf life estimation of strawberry juice stored under non-isothermal conditions was performed using a Weibullian-logistic model. A kinetic order of 1.1 was estimated as the best value to fit AA degradation under isothermal conditions and may be considered as the value for this particular medium. Moreover, the Weibullian-logistic model well fitted AA degradation under non isothermal conditions and may be used to predict shelf life under different fluctuation temperature histories. On the basis of temperature profiles considered in this paper, a retention of 46.8% and 42.7%, respectively for experimental and predicted data after 15 days were measured. Furthermore, it was showed a significant decrease of shelf life (about 5 days) for samples exposed to fluctuation temperature in comparison whit samples kept at constant temperature.     

Effect of maltodextrin addition on moisture sorption properties of khoa

Khoa is a popular traditional Indian milk product. It is used as the base material for preparation of variety of popular sweetmeats. The shelf life of this product is limited due to its high water activity (> 0.96). In the present investigation, an attempt was made to lower the a_w of khoa (25.62% moisture, 31.25% fat, 18.21% protein, 3.65% total ash and 21.29% lactose) by using maltodextrin (DE‐16) as a humectant (concentration: 0, 2, 5 and 10%; wt/wt). It was observed that the desorption curves of the product exhibited a sigmoid shape corresponding to type II, typical of many foods. At higher concentrations of maltodextrin, the isotherms shifted to the left compared to control. Among the several models chosen to test the fitness of sorption data, Guggenheim, Anderson and De Boer (GAB) and modified Mizrahi models showed the best fit as indicated by the smallest percentage root mean square values. The monolayer moisture content increased with increasing maltodextrin level, the range being 2.85–3.29 and 3.03–3.81 g/100 g solids for the two models, respectively. Caurie's slope also increased from 0.38 to 0.44, whereas nonfreezable water decreased from 4.98 to 4.01% as the maltodextrin level increased from 2 to 10%. Other critical water sorption parameters such as number of adsorbed monolayers, density of sorbed water and surface area of sorption were also obtained.     

Shelf life of ostrich (Struthio camelus) liver stored under different packaging conditions

Ostrich (Struthio camelus) liver is an important edible meat by-product. However, it has a low commercial value, and it is underutilized. The present study was conducted to establish the shelf life of ostrich liver, stored at 2 +/- 1 degrees C for 18 days, under different packing conditions. Fresh livers were sliced and packed under air exposure, vacuum, and modified atmosphere (MA: 80% CO2 plus 20% N2). Shelf-life evaluation was based on color, lipid and hemopigment oxidation, microbial counts, and sensory assessment of odor and color. Samples stored under air exposure showed the highest lipid and hemopigment oxidation rate, which was detected by higher thiobarbituric acid reactive substances values and metmyoglobin percentage and lower heme iron content than livers stored under vacuum or MA. On the basis of aerobic bacteria counts, the shelf life of ostrich liver stored under aerobic conditions would be 7 days, whereas under vacuum or MA, it would be 14 days. In livers stored under anaerobic conditions (vacuum or MA packed), lactic acid bacteria represented a significant proportion of the spoilage microbiota. Minimal changes in color perception were also obtained in vacuum-packed samples at the end of the storage period. In air-packed samples, high levels of off-odors were already perceived during the first 6 days of storage, whereas in livers stored under anaerobic conditions (vacuum and MA), these levels of off-odor were not yet perceived at that time.     

Investigation of fumigant efficacy in flour mills under real-world fumigation conditions

Fumigation experiments under laboratory conditions are common but due to a number of factors, fumigation experiments under real-world conditions are difficult and rare. This study was aimed at providing an insight into efficacy evaluations of fumigants based on insect mortality data under real-world conditions. A total of eight sulfuryl fluoride (SF) and three methyl bromide (MB) fumigations were performed in four different flour mills in the Midwestern United States. Bioassays were undertaken with all insect life stages (i.e., eggs, larvae, pupae and adults) of Tribolium castaneum (Herbst) and Plodia interpunctella (Hübner) placed inside fumigated structures. In addition, in most of the fumigations, environmental conditions (e.g., prevailing wind, temperature, and relative humidity) and gas concentrations were monitored. Complete mortality was obtained for the adults and larvae of both insect species, and for the pupae of P. interpunctella. Some T. castaneum pupae survived in all three MB fumigations and in one SF fumigation. In addition, some exposed eggs were able to reach the adult stage in one MB and four SF fumigations. The methodology and procedures presented can be used in future field studies of fumigant efficacy.     

酶法真空间歇处理脱除脐橙果皮和囊衣的研究

为降低柑橘汁胞生产中通常采用的热烫去皮酸碱脱囊衣工艺造成的环境污染和水资源浪费,选用植物酶制 剂结合真空间歇处理作为一种替代方法。根据所选酶的特性选择pH 3.5、处理温度40 ℃的条件下,研究酶添加量、 真空度、间歇方式和浸泡时间等因素对去皮效果的影响。在单因素试验的基础上确定各因素的最佳水平,并采用 L9（34）正交试验优化了各工艺参数。结果表明：在酶制剂添加量2%、真空度10 psi、间歇减压方式（2＋2＋2＋ 2）min的条件下处理50 min后,得到脐橙全果果皮去除完全、囊衣脱除干净的样品。     

橡胶缓冲垫受偏心冲击特性的数值研究

气动钉枪缓冲垫在工作过程中常受到来自枪针组件的偏心冲击。文章以气动钉枪工作状态为基础,通过ANSYS/LS-DYNA软件对缓冲垫承受偏心冲击的特性进行数值模拟研究。研究表明,在偏心冲击下,橡胶缓冲垫的损坏将加剧,提高枪针组件的对中性将有助于橡胶缓冲垫寿命的提高。     

Artificial neural network approach to simultaneously predict shelf life of two varieties of packaged rice snacks

Actual storage shelf life test by storing a packaged product under typical storage conditions is costly and time consuming. A new approach using an artificial neural network (ANN) algorithm for shelf life prediction of two varieties of moisture-sensitive rice snacks packaged in polyethylene and polypropylene bags and stored at various storage conditions was established. The ANN used to predict the shelf life was based on multilayer perceptron with back propagation algorithm. The ANN algorithm employed the data of product characteristics, package properties and storage conditions. The neural network comprised an input, one hidden and one output layers. The network was trained using Bayesian regularisation. The performance of ANN was measured using regression coefficient ( R ² = 0.23–0.28) and root mean square error (RMSE = 0.96–0.99). The ANN-predicted shelf lives agreed very well with actual shelf life data. ANN could be used as an alternative method for shelf life prediction of moisture-sensitive food products as well as product/package optimisation.     

不同贮藏温度西式火腿切片品质变化规律研究

为研究市场上低温火腿切片的质量和安全性,对不同贮藏温度的真空包装火腿切片的品质变化进行动态跟踪,分析产品在0～4、7～11℃条件下,其感官品质、菌落总数、大肠菌群、色泽、pH值、水分含量、保水性和质构特性的动态变化。结果表明：两种产品品质变化的规律大致相同。0～4℃贮藏比7～11℃产品的菌落总数增长相对缓慢,pH值、水分含量,保水性和质构特性的变化更加稳定。低温更有利于保持产品品质的稳定性和安全性,延长肉品的货架期。     

Hydrodefluorination and Hydrogenation of Fluorobenzene under Mild Aqueous Conditions

Fluorinated organic compounds are increasingly used in many applications, and their release to the environment is expected. It is therefore important to find suitable methods for degradation of fluorinated compounds under environmentally relevant conditions. In this study, a simple heterogeneous rhodium-based catalytic system (Rh/Al(2)O(3) and H(2)) for hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions (1 atm of H(2), ambient temperature) was developed and the underlying reaction mechanism was investigated. Fluorobenzene degraded rapidly (t(1/2) ≈ 0.2 h) to form cyclohexane and fluoride (F(-)) as the stable end products, with benzene and cyclohexene observed as intermediates. Cyclohexadiene intermediates were not observed but were expected to form during the hydrogenation of benzene. Three postulated but unobserved fluorinated intermediates were subjected to the catalytic reaction conditions, and it was concluded that they most likely do not form during the fluorobenzene degradation reaction. Isotope labeling experiments showed that the unsaturated intermediates undergo rapid and reversible hydrogenation/dehydrogenation under the reaction conditions and also that fully saturated compounds are unreactive in the catalytic system. Both molecular hydrogen and water were sources of hydrogen in the final cyclohexane product. Kinetic fitting indicated that sorption/desorption of fluorobenzene onto the catalyst surface plays an important role in the mechanism.     

超高压作用下的食品包装问题

超高压技术是当前备受关注,且各国广泛开展研究的一项食品高新技术.超高压食品包装材料将伴随各类食品经受高压的作用和后续的储运过程.然而目前尚未形成与HPP技术配套的包装理论与技术.本研究拟对该领域的研究现状与局限性进行探讨,进而提出其未来的研究重点和发展方向.     

Storage behaviour of minimally processed pumpkin (Cucurbita maxima) under modified atmosphere packaging conditions

 Minimally processed vegetables in fresh, ready-to-cook form are gaining the confidence of both the trader and the consumer. This has led to a need to develop technology for increasing shelf life while maintaining the microbial, nutritional and sensory quality of minimally processed vegetables. This investigation was carried out on pumpkin in minimally processed form, packed in different polymeric film bags of varying permeabilities, creating an active equilibrium modified atmosphere within the package for the extention of storage life. It was observed that minimally processed pumpkin, which has a high respiratory rate at room temperature (155.7 mg CO₂/kg/h) could be stored for a period of 25 days at 5±2  °C under modified atmosphere packaging conditions with a minimum physiological loss in weight of 0.06% and marginally low changes in biochemical constituents, such as vitamin C, total soluble solids, moisture, carotenoids and titrable acidity, enabling the retention of near-fresh quality. The microbial loads of mesophilic aerobes and coliforms, which were log 5.5 and log 4.3 were less than threshold level. There was no growth of yeasts and moulds or mesophilic spore formers at the end of the storage period. Received: 24 January 2000 / Revised version: 4 April 2000     

Performance of antioxidative compounds under frying conditions: A review

Although much study has been done assessing activity of antioxidants at ambient and accelerated storage temperatures, the results cannot correctly depict their performance under frying conditions. Due to the stringent conditions imposed, most conventional antioxidative compounds failed under frying conditions, suggesting the need for a continuous modification to improve their effectiveness. Although syntheses and performance evaluation of over a hundred (semi)synthetic antioxidants have been reported in literature, only a small fraction have been specifically designed and/or evaluated under frying conditions. Here, the performance under frying conditions of major natural and synthetic antioxidants is reviewed. The recent trend in the designing of antioxidants for frying applications is also reviewed with the view of stimulating further study in this direction.     

Effects of dietary rosemary extract on lamb spoilage under retail display conditions

A dietary rosemary extract (RE) was tested to extend the shelf life of raw lamb meat. Lambs were supplemented with 0.6 mg kg⁻¹ RE during fattening (from 13 to 25 kg live weight). Meat spoilage (total viable counts, psycrophilic bacteria, Enterobacteriaceae, molds and yeasts), TBARS, CIE L*a*b* color and the sensory traits of lamb cuts were analyzed on days 0, 7, 14 or 21 under retail display conditions (70/30 O₂/CO₂ atmosphere, 2 °C temperature and 1600 lx lighting). Supplementation of the lamb diet with RE was effective (P < 0.05) in prolonging the time chilled-packed lamb cuts could be kept under retail display conditions. Dietary rosemary clearly inhibited lipid oxidation and rancidity, and was moderately efficient in preventing sensory deterioration and microbial spoilage. Although the results concerning meat preservation were limited, the dietary use of rosemary extracts in lambs seems to be promising as a nutritional strategy for improving meat quality.     

Sulfate-Reducing Bacteria Lower Sulfur-Mediated Pitting Corrosion under Conditions of Oxygen Ingress

The effect of oxygen ingress into sour water containing dissolved sulfide on the production of sulfur and polysulfide (S-PS) and associated iron corrosion was investigated. Biotic (active SRB present), abiotic (autoclaved SRB present), and chemical (no bacteria present) conditions were compared. Under biotic conditions formation of S-PS was only seen at a high ratio of oxygen to sulfide (R(OS)) of 1 to 2.4. General corrosion rates increased 10-fold to 0.10 mm/yr under these conditions. Under abiotic and chemical conditions S-PS formation increased over the entire range of R(OS) with general corrosion rates reaching 0.06 mm/yr. Although general corrosion rates were thus highest under biotic conditions, biotically corroded coupons showed much less pitting corrosion. Maximum pit depth increased to 40-80 μm with increasing R(OS) for coupons incubated for 1 month under abiotic or chemical conditions but not for biotically incubated coupons (10 μm). This appeared to be related to the properties and size of the sulfur formed, which was hydrophobic and in excess of 10 μm under chemical or abiotic conditions and hydrophilic and 0.5 to 1 μm under biotic conditions. Hence, perhaps contrary to expectation, SRB lowered pitting corrosion rates under conditions of oxygen ingress due to their ability to respire oxygen and produce a less aggressive form of sulfur. Microbial control, which is usually required in sour systems, may be counterproductive under these conditions.     

Performance of a photochromic time–temperature indicator under simulated fresh fish supply chain conditions

The objective of this study was to investigate the performance of a photochromic time–temperature indicator (TTI) under dynamic temperature conditions simulating real fresh fish distribution chain scenarios. The work aimed at testing the possibility of extending the application of the TTI kinetic model, developed for specific temperature range of isothermal conditions, at low temperatures. The results showed that the TTI presented reproducible responses after being charged and during the discolouration process under different conditions, which revealed the reliability of the indicator. The TTI reflected well the temperature conditions of the studied scenarios, which indicates its potential application to continuously monitor the temperature history of the fresh fish supply chain. The kinetic model gave good fits in non‐abused scenarios at temperatures below 2 °C, presenting the potential for application of the model in determining the right charging level to suit a product’s shelf life at low temperatures.