Selected Quality Characteristics of Fresh‐Cut Sweet Potatoes Coated with Chitosan during 17‐Day Refrigerated Storage

ABSTRACT: Selected quality characteristics of fresh‐cut sweet potatoes (FCSP) coated with chitosan were evaluated during 17‐d refrigerated storage. The FCSP cubes were coated with a solution (1%, w/v) of chitosan having 470 or 1110 kDa. Color (L*, a*, b*) values of uncoated and chitosan‐coated FCSP during storage were generally affected by storage time as well as coating treatments (P < 0.05). No significant changes in color lightness (L*) of 470 kDa‐coated FCSP were observed during the 17‐d storage. During days 3 to 17, 470 kDa‐coated FCSP had significantly higher redness (a*) and yellowness (b*) values than did uncoated and 1110 kDa‐coated FCSP. Texture firmness of uncoated and chitosan‐coated FCSP exhibited minimal changes during the 17‐d storage. Although actual weight loss values (%) of uncoated and chitosan‐coated FCSP were not significantly different at day 17, the weight loss difference (%) between day 3 and day 17 for uncoated FCSP (3.02%) was slightly higher compared to those (2.24% to 2.26%) of chitosan‐coated FCSP. The initial total aerobic count was 4.7 log₁₀ CFU/g which then gradually increased to 8.54 and 9.67 log₁₀ CFU/g after 17 d of storage for 470 kDa‐coated and uncoated FCSP, respectively. After day 6, the total aerobic counts of uncoated FCSP were higher than those of 470 kDa‐coated FCSP. The yeast and mold count of chitosan‐coated FCSP was about 2.5 log₁₀ CFU/g at day 17. Overall, consumers could not differentiate between 470 kDa‐coated FCSP at day 17 and uncoated FCSP at day 0.     

壳聚糖涂膜对沂州木瓜贮藏品质的影响

以沂州木瓜为试材,研究壳聚糖涂膜对木瓜的保鲜作用。在室温条件下采用不同质量分数的壳聚糖溶液对沂州木瓜进行涂膜处理,测定其总糖、VC含量、感官品质、质量损失率、硬度和腐烂率的变化。结果表明：壳聚糖涂膜处理能延缓果实硬度、总糖含量、VC、质量损失率和感官品质的降低,降低果实的腐烂率,1.5%壳聚糖涂膜处理保鲜效果最好,可有效地延长沂州木瓜的保鲜期。     

钙处理结合壳聚糖涂膜对芒果贮藏品质的影响

以“桂热82”号芒果为试材,在贮藏前进行浸钙处理和壳聚糖涂膜处理。结果表明：不同浓度钙结合壳聚糖涂膜处理在一定程度均能提高芒果果实耐贮性与品质,其各项指标均优于单纯的涂膜处理。1% CaCl2+1%壳聚糖涂膜和3% CaCl2+1% 壳聚糖涂膜在贮藏期间均品质维持良好且稳定,能有效地抑制可溶性固形物的升高、可滴定酸的降低、果肉颜色的褐变、果肉硬度的下降、VC 含量的下降、果皮转黄指数的上升,其腐烂与失重也得到了较好的控制,其中1% CaCl2+1% 壳聚糖涂膜处理贮藏品质更显著。     

Growth Potential of Listeria Monocytogenes and Staphylococcus Aureus on Fresh‐Cut Tropical Fruits

The objective of this study was to evaluate the fate of Staphylococcus aureus, Listeria monocytogenes, and natural microbiota on fresh‐cut tropical fruits (pitaya, mango, papaya and pineapple) with commercial PVC film at different storage temperature (5, 13, and 25 °C). The results showed that S. aureus, L. monocytogenes, and natural microbiota increased significantly on fresh‐cut tropical fruits at 25 °C. Both pathogen and natural microbiota were able to grow on fresh‐cut tropical fruits at 13 °C. The maximum population of L. monocytogenes was higher than that of S. aureus on fresh‐cut tropical fruits. L. monocytogenes and S. aureus could survive without growth on fresh‐cut pitaya, mango, and papaya at 5 °C. The population of L. monocytogenes declined significantly on fresh‐cut pineapple at all temperature, indicating composition of fresh‐cut pineapple could inhibit growth of L. monocytogenes. However, S. aureus was still able to grow on fresh‐cut pineapple at storage temperature. Thus, this study suggests that 4 kinds of fresh‐cut tropical fruits (pitaya, mango, papaya, and pineapple) should be stored at low temperature to extend shelf life as well as to ensure the safety of fresh‐cut fruits.     

Combined Application of Antibrowning,Heat Treatment and Modified‐Atmosphere Packaging to Extend the Shelf Life of Fresh‐Cut Lotus Root

This work aimed to determine the effects of different concentrations of antibrowning treatments (that is, distilled water [DW], 1% ascorbic acid [AA], 0.5% chamomile [CM], and 1% AA + 0.5% CM) and heat‐treatment (55 °C for 45 s) combined with packaging under 4 different modified‐atmosphere gas compositions (that is, air, vacuum, 100% CO₂, 50% CO₂/50% N₂) on the quality and microbiological characteristics of fresh‐cut lotus root. The quality characteristics (that is, color, weight loss, texture, pH, polyphenoloxidase activity, and total phenolic content) of the AA + CM‐dipped sample in 100% CO₂ packaging were maintained significantly better than those of the other samples (P < 0.05). The microbiological counts observed in the DW‐dipped sample during storage were higher than those of the AA, CM, and AA + CM samples, and heat‐treatment retarded the microbiological deterioration of fresh‐cut lotus root. Therefore, the results revealed that dipping in an antibrowning treatment (AA + CM), and 100% CO₂ MAP with heat treatment effectively extend the shelf life of fresh‐cut lotus root to 21 d at 5 °C.     

Predictive Modeling for Growth of Non‐ and Cold‐adapted Listeria monocytogenes on Fresh‐cut Cantaloupe at Different Storage Temperatures

The aim of this study was to determine the growth kinetics of Listeria monocytogenes, with and without cold‐adaption, on fresh‐cut cantaloupe under different storage temperatures. Fresh‐cut samples, spot inoculated with a 4‐strain cocktail of L. monocytogenes (～3.2 log CFU/g), were exposed to constant storage temperatures held at 10, 15, 20, 25, or 30 °C. All growth curves of L. monocytogenes were fitted to the Baranyi, modified Gompertz, and Huang models. Regardless of conditions under which cells grew, the time needed to reach 5 log CFU/g decreased with the elevated storage temperature. Experimental results showed that there were no significant differences (P > 0.05) in the maximum growth rate k (log CFU/g h^?1) and lag phase duration λ (h) between the cultures of L. monocytogenes with or without previous cold‐adaption treatments. No distinct difference was observed in the growth pattern among 3 primary models at various storage temperatures. The growth curves of secondary modeling were fitted on an Arrhenius‐type model for describing the relationship between k and temperature of the L. monocytogenes on fresh‐cut cantaloupe from 10 to 30 °C. The root mean square error values of secondary models for non‐ and cold‐adapted cells were 0.018, 0.021, and 0.024, and 0.039, 0.026, and 0.017 at the modified Gompertz, Baranyi, and Huang model, respectively, indicating that these 3 models presented the good statistical fit. This study may provide valuable information to predict the growth of L. monocytogenes on fresh‐cut cantaloupes at different storage conditions.     

A Comparative Study of Natural Antimicrobial Delivery Systems for Microbial Safety and Quality of Fresh‐Cut Lettuce

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh‐cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan‐co‐poly‐N‐isopropylacrylamide (chitosan‐PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log₁₀ CFU/g (P < 0.05) compared to the other encapsulation systems when fresh‐cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan‐PNIPAAM‐CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh‐cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan‐PNIPAAM‐CBE, up to 2 log₁₀ CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan‐PNIPAAM‐CBE nanoparticles effectively inhibited spoilage microorganisms’ growth and extended fresh‐cut lettuce shelf‐life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh‐cut lettuce.     

氯化钙处理对速冻蓝莓冻藏期品质的影响

研究不同质量分数氯化钙处理对速冻蓝莓果实于－18 ℃冻藏时品质变化的影响。结果表明：随着冻藏时间延长,速冻蓝莓果实的质量、硬度、可溶性固形物（TSS）、可滴定酸、VC、花色苷和总酚含量均呈下降趋势。浸钙处理可延缓速冻蓝莓果实质量、硬度、TSS、可滴定酸、VC、花色苷和总酚含量的下降,保持果实原有品质。在整个冻藏期多酚氧化酶（PPO）和过氧化物酶（POD）活性不断下降,氯化钙处理组冻藏后期PPO活性明显被抑制,但对POD活性没有显著效果。综合分析各指标,经1.5%氯化钙溶液处理的速冻蓝莓其冻藏期品质最好。     

Impact of Mixtures of Different Fresh‐Cut Fruits on Respiration and Ethylene Production Rates

Packaging and storage of fresh‐cut fruits and vegetables are a challenging task, since fresh produce continue to respire and senesce after harvest and processing accelerates the physiological processes. The response on respiration and ethylene production rates of fresh produce to changes in O₂ and CO₂ concentrations and temperature has been extensively studied for whole fruits but literature is limited on processed and mixed fresh‐cut fruits. This study aimed to investigate the effects of mixing various proportions of fresh‐cut fruits (melon chunks, apple slices, and pineapples cubes) on respiration and ethylene production rates and to develop predictive models for modified atmosphere packaging. The experiment was designed according to a simplex lattice method and respiration and ethylene production rates were measured at 10 °C. Results showed that single component pineapple cubes, apple slices, and melon chunks, in this order, had significant constant coefficients (P = 0.05) and the greatest impact on respiration rate while the interactive binary and tertiary coefficients were insignificant. For ethylene production rates, single component apple slices, melon chunks, and pineapple cubes, and their 3‐component mixtures, in this order, had significant constant coefficients (P = 0.05) while binary coefficients were insignificant. Mathematical models were developed and validated; the cubical model was the best to describe the influence of proportion of fruit on respiration and ethylene production rates, however, considering simplicity the linear part of the model is recommended to quantify respiration and ethylene production rates of mixed fresh‐cut fruits.     

Effect of chitosan coating in preventing deterioration and preserving the quality of fresh‐cut papaya ‘Maradol’

BACKGROUND: Chitosan can form antimicrobial, semi‐permeable barriers that limit gas exchange and reduces water loss in fruits. Consumer interest in fresh‐cut papaya fruit is leading to increasing demand because of its sensorial and antioxidant properties. However, papaya is a highly perishable product that is prone to loss of weight, loss of firmness and microbial attack. The aim of this study was to evaluate the effect of chitosan coatings on the overall quality of fresh‐cut papaya. Chitosan coatings of low (LMWC), medium (MMWC) and high (HMWC) molecular weights, at concentrations of 0.01 and 0.02 g mL^?1, were applied to fresh‐cut papaya cubes. The treated cubes were stored at 5 °C and changes in quality were evaluated. RESULTS: MMWC maintained the highest color values (L* and b*) and firmness. Chitosan coatings suppressed mesophilic plate count, and the growth of molds and yeast, compared to controls. The MMWC coatings at 0.02 g mL^?1 resulted in the highest antimicrobial activity and decreased the activity of the enzymes polygalacturonase and pectin methylesterase, followed by low and high MW chitosan coatings at 0.02 g mL^?1. CONCLUSION: The application of the MMWC treatment at 0.02 g mL^?1 could be used to reduce deteriorative processes, maintain quality and increase the shelf life of fresh‐cut papaya stored at 5 °C. Copyright © 2008 Society of Chemical Industry     

Production of Volatiles in Fresh‐Cut Apple: Effect of Applying Alginate Coatings Containing Linoleic Acid or Isoleucine

One of the main quality parameters in apples is aroma, its main precursors are fatty acids (FA) and amino acids (AA). In this study, alginate edible coatings were used as carriers of linoleic acid or isoleucine to serve as precursors for the production of aroma in cut apples. Apple wedges were immersed in a CaCl₂ solution and coated with one of the following formulations: alginate solution (Alg‐Ca), Alg‐Ca‐low‐level linoleic acid (0.61 g/Lt), (LFA), Alg‐Ca‐high‐level linoleic acid (2.44 g/L; HFA), Alg‐Ca‐low‐level isoleucine (0.61 g/L; LAA), and Alg‐Ca‐high‐level isoleucine (2.44 g/L; HAA). Apple wedges were stored at 3 °C and 85% relative humidity for 21 d and key volatiles were studied during storage. Addition of precursors, mainly isoleucine, showed to increase the production of some key volatiles on coated fresh‐cut apples during storage. The concentration of 2‐methyl‐1‐butanol was 4 times higher from day 12 to day 21 in HAA, while 2‐methyl butyl acetate increased from day 12 to day 21 in HAA. After 21 d, HAA‐apples presented a 40‐fold value of 2‐methyl‐butyl acetate, compared to Alg‐Ca cut apples. Values of hexanal increased during cut apple storage when the coating carried linoleic acid, mainly on HFA, from 3 to 12 d. The ability of apples to metabolize AA and FA depends on the concentration of precursors, but also depends on key enzymes, previous apple storage, among others. Further studies should be done to better clarify the behavior of fresh‐cut apples as living tissue to metabolize precursors contained in edible coatings for the production of volatiles.     

超声波与氯化钙结合处理对牛肉品质的影响

本实验采用超声波与钙结合对牛肉进行处理,通过测定牛肉的质构、增水率、色泽、游离氨基酸含量变化以及对熟肉的感官评定,探讨超声波与钙盐结合处理对牛肉品质的影响。结果表明:超声波与钙盐结合处理能显著降低牛肉的硬度,牛肉的黏性有一定的增加,但对其他质构指标影响不大;处理后牛肉的增水率增加;在色泽方面,L*值明显增加,a*值明显降低,但对b*值影响不大;游离氨基酸含量明显增加;感官评定的总体可接受性得分也较高。     

采前喷钙对黄瓜采后冷藏品质的影响

冷害是限制黄瓜低温贮藏和运输的主要因素,以黄瓜品种‘露地二号’为试材,对黄瓜叶面进行采前喷施CaCl2,以增加黄瓜的耐冷性,研究采前喷钙对黄瓜采后冷藏（4±0.5） ℃品质的影响,为春冬两季黄瓜的长途运输和贮藏提供参考。结果表明,冷藏期间各处理冷害指数、丙二醛含量、相对电导率、脯氨酸含量冷藏期间均上升;硬度降低,色泽变暗,可溶固形物含量和主要香气物质相对含量均减少。冷藏结束时,0.75%、1% CaCl2处理黄瓜的冷害指数最小为0.3,而且丙二醛含量和相对电导率均显著低于对照（P＜0.05）;钙处理黄瓜的硬度均比对照大,CaCl2质量分数越大硬度越大。0.75%和1% CaCl2处理黄瓜含有更多的可溶性固形物,脯氨酸生成量也较多,主要的香气物质相对含量也较大,并且在贮藏期间色泽保持均比对照好。综合考虑,最终确定0.75% CaCl2处理为黄瓜喷钙的最佳质量分数,能较好地维持黄瓜采后品质,将冷害症状出现延迟了4 d。     

Effects of Ultraviolet Light (UV‐C) and Heat Treatment on the Quality of Fresh‐Cut Chokanan Mango and Josephine Pineapple

The effects of ultraviolet (UV‐C) and medium heat (70 °C) treatments on the quality of fresh‐cut Chokanan mango and Josephine pineapple were investigated. Quality attributes included physicochemical properties (pH, titratable acidity, and total soluble solids), ascorbic acid content (vitamin C), antioxidant activity, as well as microbial inactivation. Consumers’ acceptance was also investigated through sensory evaluation of the attributes (appearance, texture, aroma and taste). Furthermore, shelf‐life study of samples stored at 4 ± 1 °C was conducted for 15 d. The fresh‐cut fruits were exposed to UV‐C for 0, 15, 30, and 60 min while heat treatments were carried out at 70 °C for 0, 5, 10 and 20 min. Both UV‐C and medium heat treatments resulted in no significant changes to the physicochemical attributes of both fruits. The ascorbic acid content of UV‐C treated fruits was unaffected; however, medium heat treatment resulted in deterioration of ascorbic acids in both fruits. The antioxidants were enhanced with UV‐C treatment which could prove invaluable to consumers. Heat treatments on the other hand resulted in decreased antioxidant activities. Microbial count in both fruits was significantly reduced by both treatments. The shelf life of the fresh‐cut fruits were also successfully extended to a maximum of 15 d following treatments. As for consumers’ acceptance, UV‐C treated fruits were the most accepted as compared to their heat‐treated counterparts. The results obtained through this study support the use of UV‐C treatment for better retention of quality, effective microbial inactivation and enhancement of health promoting compounds for the benefit of consumers.     

超声结合氯化钙溶液处理对牛肉品质的影响

探讨超声波结合氯化钙处理在不同成熟期对牛肉色泽、系水力、蒸煮损失及嫩度的影响。选择对宰后12h成年母黄牛的臀肉注射300mmol/L 氯化钙(注射量分别为肉质量的5%、10%),样品再分别在强度为133W/m2 的超声波中处理6、12min,即4 个处理组(Ⅰ组注射量5%、处理6min,Ⅱ组注射量5%、处理12min,Ⅲ组注射量10%、处理6min,Ⅳ组注射量10%、处理12min),对照组未作任何处理。各组分别在4℃成熟1、2、3、4、5、7d时检测肉块的色泽、系水力、蒸煮损失及嫩度(剪切力)。结果表明：注射10% 氯化钙结合超声波处理12min 对牛肉的色泽、系水力、蒸煮损失改善效果最好,注射5% 氯化钙结合超声波处理6min 对改善嫩度效果最显著(P ＜0.05),剪切力平均降低了28.41%。所以超声波结合氯化钙处理牛肉能明显改善牛肉品质。     

E: Food Engineering & Physical Properties. Effect of Supercritical Carbon Dioxide Pasteurization on Natural Microbiota,Texture, and Microstructure of Fresh‐Cut Coconut

Abstract: The objective of the present study was the evaluation of the effectiveness of supercritical carbon dioxide (SC‐CO₂) as a nonthermal technology for the pasteurization of fresh‐cut coconut, as an example of ready‐to‐eat and minimally processed food. First, the inactivation kinetics of microbiota on coconut were determined using SC‐CO₂ treatments (pressures at 8 and 12 MPa, temperatures from 24 to 45 °C, treatment times from 5 to 60 min). Second, the effects of SC‐CO₂ on the hardness and microstructure of fresh‐cut coconut processed at the optimal conditions for microbial reduction were investigated. SC‐CO₂ treatment of 15 min at 45 °C and 12 MPa induced 4 log CFU/g reductions of mesophilic microorganisms, lactic acid bacteria, total coliforms, and yeasts and molds. The hardness of coconut was not affected by the treatment but the samples developed an irregular and disorderly microstructure. Results suggested the potential of SC‐CO₂ in preserving fresh‐cut fruits and ready‐to‐eat products. Practical Application: The effectiveness of SC‐CO₂ as a nonthermal technology for the pasteurization of fresh‐cut coconut was studied. The results demonstrated the possibility to apply the treatment as a method to induce the inactivation of the natural microorganisms, preventing the microbial spoilage and, at the same time, preserving the hardness of the product. The available data will give a valuable input to the fresh‐cut fruits industry.