Effect of different pre-treatments and dehydration methods on quality characteristics and storage stability of tomato powder

Dehydration process was carried out for tomato slices of var. Avinash after giving different pre-treatments such as calcium chloride (CaCl₂), potassium metabisulphite (KMS), calcium chloride and potassium metabisulphite (CaCl₂+KMS), and sodium chloride (NaCl). Untreated samples served as control. Solar drier and continuous conveyor (tunnel) drier were used for dehydration. Quality characteristics of tomato slices viz. moisture content, sugar, titratable acidity, lycopene content, dehydration ratio, rehydration ratio and non-enzymatic browning (NEB) as affected by dehydration process were studied. Storage study was also carried out for a period of 6 months for tomato powder packed into different types of packaging materials viz. metalized polyester (MP) film and low density polyethylene. Changes in lycopene content and NEB were estimated during storage at room temperature. Pre-treatment of 5 mm thickness of tomato slices with CaCl₂ in combination with KMS and drying using a tunnel drier with subsequent storage of product in MP bags was selected as the best process.     

Influence of different treatments on dehydrated cauliflower quality

Fresh cauliflower was cut into florets, blanched, treated and spread in trays to dry by means of a solar drying process. The influences of packaging materials, blanching time, and potassium metabisulphite (KMS) concentration levels on the quality of solar dehydrated cauliflower up to 6 months of storage were studied. Ascorbic acid (vitamin C) present in fresh cauliflower was 74.61 mg (100 g)^?1. Results revealed that ascorbic acid concentration decreased with an increase in blanching time but its retention was high in cauliflower dehydrated by solar drying. Dehydrated cauliflower had 581.37 mg (100 g)^?1 of ascorbic acid in samples treated with 0.5, 1.0 and 1.5% of KMS with 3 min blanching at day zero. Washing cauliflower florets in tap water reduced the microbial load as compared with the unwashed sample. Processed and dehydrated cauliflower, packed in three types of packaging materials did not show presence of fungi even after storage for 6 months. In almost all samples, permissible levels of bacterial counts were observed after 6 months of storage. All the samples were also found to be free from Escherichia coli. It was found that blanched samples (blanching done for 7 min) treated with 0.5% KMS, dehydrated and then packed in laminated aluminium foil (LF) were the best in regard with nutritional and microbiological quality of dehydrated cauliflower.     

热风真空组合干燥苹果片试验研究

以苹果为原料,通过试验探讨了在热风真空组合干燥条件下,热风温度、热风时间、真空温度、真空度等因素对热风真空组合干燥苹果片品质的影响。结果表明:热风真空组合干燥较热风干燥而言可有效提高其干制品的质量;热风真空组合干燥苹果片较优的工艺参数为:热风温度60℃、热风时间1h,真空温度50℃、真空度30kPa。     

真空微波与热风联合干燥蒜片的工艺研究

运用正交实验对四种无硫护色液进行复合实验,最佳护色组合为：CaCl2浓度为0.6%、NaCl浓度为0.8%、L-半胱氨酸浓度为0.10%,经此复合护色液护色得到干燥蒜片L＊值为86.23。比较了热风、真空微波、真空微波与热风联合干燥三种生产工艺所得蒜片干制产品的品质,采用正交实验优化了热风与真空微波联合干燥蒜片的生产工艺。结果表明：前期采用真空度-90kPa,微波功率375W,微波干燥20min,后期60℃热风干燥60min,干燥总时间为80min,缩短了热风干燥时间,得到了高品质的蒜片产品。     

枣片的预处理及干燥方式研究

以木枣为实验材料,探讨不同的脱水预处理和干燥方式对枣片品质的影响。采用真空渗糖的方式对枣片进行脱水预处理,改变糖的种类和配比,对经预处理和干燥后的枣片进行综合评定,选择出一种较佳的糖液配方和干燥方式。研究结果表明,糖液的最佳配比为25%蔗糖、35%葡萄糖,产品的综合得分高达96.87。采用真空低温方法干燥枣片,所得产品品质较佳、加工时间短。     

Effects of onion on physicochemical properties,lipid oxidation and microbial growth of fresh pork patties

Onions with or without heating (100 °C, 30 min) were extracted with water or methanol, and antioxidant and antimicrobial activities of onion extracts were evaluated. Product characteristics of fresh pork patties containing various onion extracts were measured during refrigerated storage. Water extracts of onions showed higher extraction yield and iron chelating ability than methanol extracts (P < 0.05), whereas, the latter was more effective than the former in phenolic compounds and reducing power (P < 0.05). The addition of onion extracts [water extract from fresh onion (WEFO), methanol extract from heated onion (MEHO) and their combinations (WEFMEHO)] to pork patties decreased redness, increased yellowness, and inhibited lipid peroxidation (P < 0.05). One per cent of WEFMEHO in pork patties had antioxidant activities as effective as butylated hydroxyl toluene (BHT, 0.01%). Redness and yellowness decreased and increased with the addition of onion extract, respectively (P < 0.05).     

Influence of moderate heat pre-treatments on physical and chemical characteristics of kiwifruit slices

The effect of mild heat treatments, applied to whole kiwifruit, on physical characteristics and chemical composition of minimally processed fruit was studied. Fruits were subjected to heat treatments at 45 °C for 25 and 75 min, cooled for 24 h, minimally processed and stored at 4 °C for 12 days. Heat-treated fruits showed increased respiration rates in the first 2 days of storage. Samples colour was marginally affected either by heat treatments or by minimal processing. The application of heat treatments leads to an increment of slices firmness due to cross linking between demethylated galacturonic acid chains and endogenous calcium. An increment in sucrose, L-malic, citric, quinic and ascorbic acids was observed as a consequence of applied heat treatments. Heat treatment at 45 °C for 25 min applied to whole fruits allows quality retention of minimally processed fruit during 9 days at 4 °C.     

Experimental study on drying of pear slices in a convective dryer

The experiments were conducted on pear slices with thickness of 5 mm at temperatures of 50, 57, 64 and 71 °C with an air velocity of 2.0 m s^?1. Prior to drying, pear slices were pretreated with citric acid solution (0.5% w/w, 1 min, 20 °C) or blanched in hot water (1 min, 85 °C). Also, the untreated samples were dried as control. The shortest drying time of pear slices was obtained with pretreatment with citric acid solution. It was observed that whole drying process of pear slices took place in a falling rate period. Four mathematical models were tested to fit drying data of pear slices. According to the statistical criteria (R², χ² and RMSE), the Midilli et al. model was found to be the best model to describe the drying behaviour of pear slices. The effective diffusivity of moisture transfer during drying process varied between 8.56 × 10^?11 and 2.25 × 10^?10 m² s^?1, while the activation energy of moisture diffusion in pear slices was found to be 34.95–41.00 kJ mol^?1.     

Effect of blanching and drying treatments on quality of bamboo shoot slices

The enzymes activity, texture, pectin, microstructure and colour change in bamboo shoots (Dendrocalamus latiflorus) were examined to evaluate the effect of blanching and drying treatments on quality of bamboo shoot slices (BSS). Peroxidase (POD), phenylalanine ammonia‐lyase and polyphenol oxidase in BSS will become completely inactive at 95 °C for 6‐, 9‐ and 12‐min blanching treatments, respectively. The hardness and protopectin (PP) content decreased after the blanching treatment. Meanwhile, the content of water‐soluble pectin increased initially and then decreased gradually during the blanching. After the blanching treatment, the L* and a* of BSS decreased, while b* increased, ΔE > 2. The hardness of rehydrated BSS decreased by 43.57% after freeze drying (FD), which, however, decreased more after hot air drying (HAD). The pectin of rehydrated BSS was also determined to explain the hardness change in BSS. The BSS acquired similar microstructure of fresh samples after FD, while microstructure of BSS was severely damaged after HAD. The colour of BSS changes significantly after drying treatment. However, FD can maintain better colour of BSS than HAD. The results may provide a reference for industrial production of BSS.     

Effects of grape seed extract on the oxidative and microbial stability of restructured mutton slices

The antioxidant and antimicrobial efficacy of grape seed extract (GSE) was studied in restructured mutton slices (RMS) under aerobic and vacuum packaging conditions during refrigerated storage. The RMS treated with grape seed extract (GSE) had significantly (P < 0.05) lower thiobarbituric acid reactive substance (TBARS) values and free fatty acids (FFA) % compared to control (C) and butylated hydroxy anisole (BHA) treated RMS during storage at 4 ± 1 °C. Addition of GSE significantly (P < 0.05) reduced the total psychrophilic and coliform counts in RMS during refrigerated storage. The GSE treated mutton slices recorded significantly (P < 0.05) superior scores of color, flavor, juiciness and overall palatability than C and BHA treated RMS. The TBARS values, FFA % and microbial counts increased significantly (P < 0.05) during storage. It can be concluded that GSE has excellent antioxidant and antimicrobial properties compared to control and BHA treated RMS during refrigerated storage under aerobic and vacuum conditions.     

Physicochemical and microbial quality evaluation of foam‐mat‐dried pineapple powder

Present experiments were carried to study the physicochemical and microbial quality of foam‐mat‐dried pineapple powder. Pineapple pulp was foamed using two foaming agents, tricalcium phosphate (TCP) (0%, 0.25%, 0.50%, 0.75%, and 1.0%) and egg white (EW) (0%, 0.50%, 1.0%, 1.50%, and 2.0%). Carboxy methyl cellulose (0.25%) was used as foam stabiliser, and drying was carried out at 65, 75, and 85 °C in tray drier followed by pulverising the dried foam mats in to fine powder. Powdered samples were analysed for various physicochemical quality parameters viz. total sugars, reducing sugars, ascorbic acid, total acid, pH, iron, phosphorus and calcium content, and bacterial and fungal load. Statistical analysis using LSD revealed that sample dried using 1% TCP at 65 °C was the best with 4.60% total sugars, 2.71% reducing sugars, 4.05 mg per 100 g ascorbic acid, 0.35% total acid, 0.29 mg per 100 g Iron, 2.24 mg per 100 g phosphorous, and 6.58 g per 100 g calcium and zero bacterial and fungal growth.     

护色处理和膨化干燥工艺对苹果脆片品质的影响

探讨苹果变温压差膨化干燥条件对苹果脆片品质的影响。采用蒸馏法检测硫的残留量。以硫的残留量和色泽系数L、a、b值为指标,研究亚硫酸盐护色处理和膨化工艺对苹果脆片硫残留量和产品色泽的影响。结果表明,变温压差膨化干燥方法具有较高脱硫能力。使用0.02%亚硫酸酸钠护色处理的苹果,采用膨化工艺Ⅲ进行膨化干燥制备的苹果脆片中硫残留量符合国家标准GB 2760——2007,具有良好色泽和酥脆口感。     

Effect of salt and sucrose content on dielectric properties and microwave freeze drying behavior of re-structured potato slices

Potato puree was used to prepare re-structured potato slices. The effect of salt and sucrose content on microwave freeze drying (MFD) and the variation of the dielectric properties of the potato slices were studied. Results showed that the dielectric constant (ε′) and loss factor (ε″) of the potato purees decreased significantly after freezing. Both salt and sucrose addition increased ε′ and ε″ of the samples at low temperatures (−25 to −5 °C). The salt content had greater influence relative to sucrose content on dielectric properties of the samples. Sucrose addition shows insignificant influence on dielectric properties of the thawing samples; while for the salted samples, ε′ decreased gradually with increasing salt content and ε″ increased significantly with increasing salt content and temperature. MFD drying rate was significant higher after adding salt and sugar.     

Influence of homogenisation conditions and drying method on physicochemical properties of dehydrated emulsions containing different solid components

Dehydrated o/w emulsions containing sodium caseinate and lactose (sample 1), and gelatine, sucrose and maltodextrin (DE 10) (sample 2) were used to study the influence of homogenisation conditions – homogenisation pressure (15 and 70 MPa) and number of passes (1 and 2) – and the drying method – spray‐drying vs. freeze‐drying – on physicochemical parameters, including oil microencapsulation efficiency (ME), oil droplet size in reconstituted emulsions, water activity, glass transition temperature, powder bulk density and time for emulsion reconstitution in water. Results showed that small and uniform oil droplets attained with increased homogenisation pressure were not sufficient for high oil encapsulation. The permeability of the solid wall to the extraction solvent appeared to be the dominant factor, and this may increase with homogenisation pressure. With the exception of oil droplet size in sample 1 and ME in sample 2, the drying method exerted larger changes in the physicochemical parameters studied than the homogenisation pressure. For sample 2, significant changes in the ME were not observed between the freeze‐dried and spray‐dried samples, even though a great emulsion destabilisation was observed in the reconstituted emulsion of the latter.     

Effect of minimal processing operations on the quality of garlic,green onion,soybean sprouts and watercress

The effect of unit operational procedures on the quality of minimally processed vegetables was investigated. Peeling methods were studied for garlic, while different preparation forms were tried for garlic, green onion and soybean sprouts. Washing and a mild heat treatment, at 60°C for 30 s, were investigated as measures to reduce microbial populations of minimally processed vegetables. With garlic it was found that dry peeling was better than wet peeling in reducing microbial populations and preserving ascorbic acid content. Removal of the root, a potential source for microbial contamination, reduced microbial load in garlic. For garlic and green onion, microbial quality deteriorated with severity of cutting. Washing reduced microbial counts of prepared vegetables. Repeated washing and use of chilled water further reduced the counts. A mild heat treat-ment markedly reduced microbial counts in soybean sprouts and watercress, which were highly loaded with microorganisms. Sensitivities of vegetables to heat treatment differ and may limit the usefulness of heat treatment for some products. © 1998 SCI.     

响应面分析热风微波耦合干燥胡萝卜片的形变

为减少干燥过程中的能耗,提高产品体积保留率,提出微波热风耦合干燥方法,运用响应面分析法对影响因素进行优化,提出干燥收缩数学模型,优化参数结果为微波功率密度1.9 w/g,热风温度65℃,胡萝卜片厚度5 mm为最佳组合参数,该参数下体积保留率提高10%,同时干燥能耗是传统热风干燥的21.27%.     

Influence of yeast culture on ruminal microbial metabolism in continuous culture

A continuous culture study was conducted to evaluate the effect of two different yeast cultures on ruminal microbial metabolism. The treatments were a) control lactation ration, b) yeast culture 1 (YC1, Diamond-V XP) and c) yeast culture 2 (YC2, A-Max), both fed at an equivalent of 57 g/head per day. The results showed that both yeast culture products increased dry matter (DM) digestion, propionic acid production, and protein digestion compared with the control. Yeast culture 1 demonstrated an increase in molar percentage of propionic acid, a reduction in acetic acid, and a lower mean nadir (daily low) pH compared with YC2. Ruminal cultures treated with YC digested more protein and contributed less bypass N than control. Supplementing YC2 resulted in a tendency for higher microbial N/kg DM digestion than YC1. Yeast culture 1 resulted in production of rumen microbes containing less protein and more ash than YC2. These results support previous research findings that yeast culture does influence microbial metabolism, and specific yeast cultures may have different modes of action.     

Effect of cassava starch gel,fish gel and mixed gels and thermal treatment on structure development and various quality parameters in microwave vacuum-dried gel slices

Three types of gels including tapioca starch gel, fish gel and mixed gels of both (cassava starch: fish = 1:1) were prepared under different thermal conditions. Slices (4 mm thick) derived from these the gels were dehydrated to a final moisture content of 7% in a microwave vacuum dryer. The micro/macro structure and selected quality parameters of the dried gel chips were measured e.g. shape, relative volume, bulk density, texture, color, sensory and microstructure. The measured gel characteristics were analyzed and related to structure development and selected quality attributes. Both fish and mixed gel chips expanded in both diameter and thickness while the starch gel chips shrank in diameter, but expanded in thickness; the former two represented a continuous cross-section composed of a cellular structure and expanded uniformly in thickness while the latter developed an open cross-section and the center expanded more than the edge region, indicative of a disc and pillow shape, respectively. The higher severity of thermal treatment favored greater expansion and reduced hardness and bulk density, and increased crispness in the mixed gel chips; they developed a smooth and fine surface and pore wall but decreased lightness and whiteness due to starch gelatinization in the starch and mixed gel chips. Only the partial dried mixed gel chips are acceptable to the panelists. A homogenous co-gel in the mixed gel contributed to the higher uniform expansion and cellular structure. These findings will help developing the restructured microwave vacuum-dried product by blending the starch with the fish.     

Influence of modified blanching treatments on inactivation of Salmonella during drying and storage of carrot slices

Documented outbreaks of human illness associated with consumption of minimally processed produce have increased in recent years. This study evaluated the influence of modified treatments on inactivation of Salmonella during preparation, home-type dehydration (60 degrees C, 6h) and storage of carrot slices. Inoculated (five strains, 7.8 log cfu/g) slices were subjected to the following treatments: (i) untreated control, (ii) steam blanching (88 degrees C, 10 min), (iii) water blanching (88 degrees C, 4 min), (iv) blanching in a 0.105% citric acid solution (88 degrees C, 4 min), or (v) blanching in a 0.21% citric acid solution (88 degrees C, 4 min), dried for 6h at 60 degrees C (140 degrees F), and stored for up to 30 d. Bacterial populations were reduced by 3.8-4.1, 4.6-5.1 and 4.2-4.6 log cfu/g immediately following steam, water or citric acid blanching, respectively. After 6h of dehydration, total reductions were 1.6-1.7 (control), 4.0-5.0 (steam blanched), 4.1-4.6 (water blanched) and 4.9-5.4 (blanched in citric acid solution) log cfu/g. Populations continued to decrease throughout storage, but were still detectable by direct plating at 30 d on all samples except for those blanched in 0.21% citric acid. Results suggest that blanching carrot slices, particularly blanching in 0.21% citric acid, before drying should enhance inactivation of Salmonella during home-type dehydration and storage.