Phenolic content and antioxidant activity of cantaloupe (cucumis melo) methanolic extracts

The objectives of this study were to determine phenolic content and antioxidant activity of methanolic extracts from different parts of cantaloupe (leaf, stem, skin, seed and flesh). The flesh extract afforded the highest yield (89.6 ± 0.3%) whilst the lowest yield was obtained from the seed (13.7 ± 0.5%) (p < 0.05). The leaf extract showed the highest total phenolic content (26.4 ± 0.3 mg GAE/g extract) and total flavonoid content (69.7 ± 3.37 μg RE/g extract) accompanied with best antioxidant activity through all antioxidant assays (p < 0.05). In addition, the stem extract also exhibited good antioxidant activity. Thus, these results suggest that methanolic extracts of cantaloupe leaf and stem may serve as a potential source of natural antioxidant for food and nutraceutical application.     

Growth kinetics of Listeria monocytogenes and spoilage microorganisms in fresh-cut cantaloupe

The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.     

甜瓜发酵饮料的研究

以甜瓜为原料,研究具有甜瓜特殊风味的乳酸菌发酵饮料。采用驯化的保加利亚乳杆菌和嗜热链球菌（1：1）为发酵菌种,通过正交试验确定最佳发酵条件为：白砂糖4％,奶粉5％,发酵温度42℃,接种量4％,发酵时间48h。稳定剂选CMC＋黄原胶1：1混合,用量为0．2％。研制的产品口感细腻,酸味可口,风味独特,是营养保健型发酵饮品。     

Uneven distribution of microorganisms on the surface of field-grown cantaloupes

Cantaloupes have been implicated in a number of foodborne illness outbreaks due to contamination with human pathogens. However, we have limited understanding on the potential microbial contamination routes, especially in the production fields. We hypothesized that the soil upon which cantaloupe fruit rest can be a source of microbial contamination. Microbial populations on the surfaces of field-grown cantaloupes were enumerated and the effect of washing on the removal of microorganisms from the cantaloupe surfaces was evaluated. The microbial populations on the lower surface (in direct contact with soil) of the cantaloupes were significantly higher (p < 0.05), averaging 2.21 log CFU/cm² (aerobic bacteria); 1.62 log CFU/cm² (coliforms); and 2.02 log CFU/cm² (molds and yeasts), compared to those on the upper surface (exposed to the air). Washing significantly reduced only the populations of yeasts and molds on the lower surfaces of cantaloupes. Scanning electron micrographs showed more microbe-like bodies on the lower surface of cantaloupe than on the top. This study revealed an uneven distribution of microbial populations on the surfaces of field-grown cantaloupes, suggesting that direct contact with soil can be a major source of microbial contamination to fruits. Field production practices that minimize direct contact of cantaloupes with the soil may serve as a control strategy for ensuring a safer product. Also, more effective surface cleaning methods should be explored.     

Growth and biofilm formation by Listeria monocytogenes in cantaloupe flesh and peel extracts on four food-contact surfaces at 22 °C and 10 °C

The nationwide listeriosis outbreak that occurred in the United States during 2011 highlighted the importance of preventing cantaloupe contamination with Listeria monocytogenes (Lm) within farm and processing environments. The objectives of this study were to determine the effects of strain and temperature on growth and biofilm formation of Lm in cantaloupe flesh and peel extracts on different food-contact surfaces. Growth of Lm strains was markedly greater at high concentration of cantaloupe extracts and temperature in comparison to low concentration and temperature. For 50 mg/ml of cantaloupe extract inoculated with 3 log CFU/ml, the growth of Lm was 8.5 log CFU/ml in 32 h at 22 °C and 6–7 log CFU/ml in 72 h at 10 °C. For 2 mg/ml of cantaloupe extract that was inoculated with Lm, the growth was 7–7.5 log CFU/ml in 72 h at 22 °C and 3.5 log CFU/ml in 72 h at 10 °C. There were no differences (P > 0.05) among Lm strains for biofilm formation in cantaloupe extracts, but biofilm formation was greater at high temperature and high concentration. For 50 mg/ml cantaloupe extracts inoculated with 3 log CFU/ml, the biofilm formation of Lm on stainless steel surface was approximately 7 log CFU/coupon at 22 °C in 4–7 days and 5–6 log CFU/coupon at 10 °C in 7 days. For 2 mg/ml cantaloupe extracts, the biofilm formation of Lm on the stainless-steel surface was approximately 5–6 log CFU/coupon at 22 °C and 4–4.5 log CFU/coupon at 10 °C in 7 days. The biofilm formation by cantaloupe outbreak strain Lm 2011L-2625 in cantaloupe extracts was least on buna-n rubber when compared to stainless steel, polyethylene and polyurethane surfaces (P < 0.05). These findings show that a very low concentration of nutrients from cantaloupe flesh or peel can induce Lm growth and subsequent biofilm formation on different food-contact processing surfaces.     

High hydrostatic pressure (HHP) inactivation of foodborne pathogens in low‐acid juices

Consumption of unpasteurised fruit/vegetable juices has increased in recent years due to their freshness, low calorie contribution and good nutritional quality. However, unpasteurised fresh juices with low acidity (pH > 4.6) and high water activity (a_w > 0.85) can support the growth of pathogens. Hence, pasteurisation is a necessary process in the production of low‐acid juices. Consumer demand has required minimally processed high‐quality foods that are free from additives, that are fresh tasting and microbiologically safe, and with an extended shelf life. High hydrostatic pressure (HHP) treatment is considered to be an alternative to thermal pasteurisation for fruit and vegetable juices. HHP treatment could preserve nutritional value and the sensory properties of fruits and vegetables due to its limited effect on the covalent bonds of low‐molecular‐mass compounds such as colour, flavour compounds and vitamins. However, inactivation of important foodborne pathogens in low‐acid foods by HHP is most urgent and critical. More research should be performed in order to satisfy consumer demands for fresh‐tasting products while retaining safety.