Quality of fresh and fresh-cut produce impacted by nonthermal physical technologies intended to enhance microbial safety

Recent developments in applications of physical fields for microbial decontamination and enhancing nutritional properties of germinated edible seeds and sprouts: a review

Germinated edible seeds and sprouts have attracted consumers because of their nutritional values and health benefits. To ensure the microbial safety of the seed and sprout, emerging processing methods involving physical fields (PFs), having the characteristics of high efficiency and environmental safety, are increasingly proposed as effective decontamination processing technologies. This review summarizes recent progress on the application of PFs to germinating edible seeds, including their impact on microbial decontamination and nutritional quality and the associated influencing mechanisms in germination. The effectiveness, application scope, and limitation of the various physical techniques, including ultrasound, microwave, radio frequency, infrared heating, irradiation, pulsed light, plasma, and high-pressure processing, are symmetrically reviewed. Good application potential for improving seed germination and sprout growth is also described for promoting the accumulation of bioactive compounds in sprouts, and subsequently enhancing the antioxidant capacity under favorable PFs processing conditions. Moreover, the challenges and future directions of PFs in the application to germinated edible seeds are finally proposed. This review also attempts to provide an in-depth understanding of the effects of PFs on microbial safety and changes in nutritional properties of germinating edible seeds and a theoretical reference for the future development of PFs in processing safe sprouted seeds.

Antimicrobial function of yeast against pathogenic and spoilage microorganisms via either antagonism or encapsulation: A review

Contaminations of pathogenic and spoilage microbes on foods are threatening food safety and quality, highlighting the importance of developing antimicrobial agents. According to different working mechanisms, the antimicrobial activities of yeast-based agents were summarized from two aspects: antagonism and encapsulation. Antagonistic yeasts are usually applied as biocontrol agents for the preservation of fruits and vegetables via inactivating spoilage microbes, usually phytopathogens. This review systematically summarized various species of antagonistic yeasts, potential combinations to improve the antimicrobial efficiency, and the antagonistic mechanisms. The wide applications of the antagonistic yeasts are significantly limited by undesirable antimicrobial efficiency, poor environmental resistance, and a narrow antimicrobial spectrum. Another strategy for achieving effective antimicrobial activity is to encapsulate various chemical antimicrobial agents into a yeast-based carrier that has been previously inactivated. This is accomplished by immersing the dead yeast cells with porous structure in an antimicrobial suspension and applying high vacuum pressure to allow the agents to diffuse inside the yeast cells. Typical antimicrobial agents encapsulated in the yeast carriers have been reviewed, including chlorine-based biocides, antimicrobial essential oils, and photosensitizers. Benefiting from the existence of the inactive yeast carrier, the antimicrobial efficiencies and functional durability of the encapsulated antimicrobial agents, such as chlorine-based agents, essential oils, and photosensitizers, are significantly improved compared with the unencapsulated ones.

Phototreatment (below 1100 nm) improving quality attributes of fresh-cut fruits and vegetables: A review

The emerging area of phototreatment technology has shown a significant potential to enhance the quality of fresh-cut fruit and vegetable products (FFVP). This review critically evaluates relevant literatures to address the potential for phototreatment technology (Red, blue, green, ultraviolet and pulsed light) applied to FFVP, outline the key to the success of phototreatment processing, and discuss the corresponding problems for phototreatment processing along with research and development needs. Base on photothermal, photophysical and photochemical process, phototreatment displays a great potential to maintain quality attributes of FFVP. The operating parameters of light, the surface properties and matrix components of the targeted material and the equipment design affect the quality of the fresh-cut products. To adapt current phototreatment technology to industrial FFVP processing, it is necessary to offset some limitations, especially control of harmful substances (For example, nitrite and furan) produced by phototreatment, comparison between different phototreatment technologies, and establishment of mathematical models/databases.

Emerging Postharvest Technologies to Enhance the Shelf-Life of Fruit and Vegetables: An Overview

Quality losses in fresh produce throughout the postharvest phase are often due to the inappropriate use of preservation technologies. In the last few decades, besides the traditional approaches, advanced postharvest physical and chemical treatments (active packaging, dipping, vacuum impregnation, conventional heating, pulsed electric field, high hydrostatic pressure, and cold plasma) and biocontrol techniques have been implemented to preserve the nutritional value and safety of fresh produce. The application of these methodologies after harvesting is useful when addressing quality loss due to the long duration when transporting products to distant markets. Among the emerging technologies and contactless and non-destructive techniques for quality monitoring (image analysis, electronic noses, and near-infrared spectroscopy) present numerous advantages over the traditional, destructive methods. The present review paper has grouped original studies within the topic of advanced postharvest technologies, to preserve quality and reduce losses and waste in fresh produce. Moreover, the effectiveness and advantages of some contactless and non-destructive methodologies for monitoring the quality of fruit and vegetables will also be discussed and compared to the traditional methods.

Impact of irradiation on physico-chemical and nutritional properties of fruits and vegetables: A mini review

Background

Fruits and vegetables are healthy because they contain good nutrients and secondary metabolites that keep the body healthy and disease-free. Post-harvest losses of fresh fruits and vegetables limit access and availability as a result of foodborne infections and poor storage technologies. The selection of fruits and vegetables depend on the starting microbial load, the size of fruits and vegetables, and the type of infrastructure.

Scope and approach

Despite the positive impacts of conventional thermal (roasting, boiling, blanching) and some non-thermal processing techniques such as High Pressure Processing (HPP), Pulse Electric Field (PEF), Cold Plasma Technology (CPT) on shelf-life extension, their use is commonly associated with a number of negative consequences on product quality such as cold plasma treatment increases the acidity and rate of lipid oxidation and further decrease the colour intensity and firmness of products. Similarly, in high pressure processing and pulse electric field there is no spore inactivation and they further limit their application to semi-moist and liquid foods. On that account, food irradiation, a non-thermal technique, is currently being used for post-harvest preservation, which could be very useful in retaining the keeping quality of various fresh and dehydrated products without negatively affecting their versatility and physico-chemical, nutritional and sensory properties.

Conclusion

Existing studies have communicated the effective influence of irradiation technology on nutritional, sensory, and physico-chemical properties of multiple fruits and vegetables accompanying consequential deduction in microbial load throughout the storage period. Food irradiation can be recognized as a prevalent, safe and promising technology however, still is not fully exploited on a magnified scale. The consumer acceptance of processed products has always been a significant challenge for innovative food processing technologies such as food irradiation. Therefore, owing to current review, additional scientific evidences and efforts are still demanded for increasing its technological request.

Use of Ultrasonic Cleaning Technology in the Whole Process of Fruit and Vegetable Processing

In an era of rapid technological development, ultrasound technology is being used in a wide range of industries. The use of ultrasound technology in fruit and vegetable processing to improve production efficiency and product quality has been an important research topic. The cleaning of whole fresh fruits and vegetables is an important part of fruit and vegetable processing. This paper discusses the development process of components of the ultrasonic equipment, the application of ultrasonic technology in fruit and vegetable cleaning, and the research advances in ultrasonic cleaning technology. Moreover, the feasibility of ultrasonication of fruits and vegetables for cleaning from the perspectives of microbial inactivation, commodity storage, and sensory analysis were discussed. Finally, the paper identified the inevitable disadvantages of cavitation noise, erosion, and tissue damage in fruit and vegetable processing and points out the future directions of ultrasonic fruit and vegetable cleaning technology.

Anti-browning effects of citronellal on fresh-cut taro (Colocasia esculenta) slices under cold storage condition

The browning on the cut surface is a big problem reducing the quality of fresh-cut taro (FCT), which causes severe postharvest losses and may raise environmental impacts. Citronellal (CA) is a natural compound in several aromatic plants. This study investigated the effects of CA treatments in different concentrations (0.2, 0.5, and 1 mL/L) on the browning of FCT under cold storage at 5°C. The results indicated that low-dose (0.2 mL/L) CA treatment showed best anti-browning effects, reflecting at the maintained L* values but the reduced a*, b* and browning index values by CA treatment during cold storage. A repeated experiment using 0.2 mL/L CA confirmed fine anti-browning effects again. Furthermore, CA (0.2 mL/L) treatment markedly reduced the contents of total phenolic compounds and soluble quinones, restrained the activities of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase, down-regulated the gene expression of 18 browning-related enzymes in FCT. These results together strongly demonstrate the validity of CA on FCT browning prevention. Given that CA is a natural compound existing in plants, low concentration of CA possesses strong anti-browning effects on FCT and also inhibitory effects on pathogens, implying that its application has potentiality to preserve high quality of fresh-cut produce for processing and storage. Moreover, CA treatment significantly decreased malondialdehyde contents and lipoxygenase activity. Correlation analysis indicated that the lipid peroxidation of cell membrane was mostly correlated with FCT browning. The results suggest that membrane lipid peroxidation was a possible reason for FCT browning and CA treatment reduced browning, in part, through alleviating the lipid peroxidation of cell membrane. Overall, our results demonstrate that CA is a novel browning mitigator for FCT under cold storage condition.

Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser

BACKGROUND

Pulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae.

METHODS

UV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5-300 mW, which corresponded to UV doses of 5-80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation.

RESULTS

The mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time.

CONCLUSIONS

A high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation.

Gaseous ozone to preserve quality and enhance microbial safety of fresh produce: Recent developments and research needs

Fresh fruits and vegetables are highly perishable and are subject to large postharvest losses due to physiological (senescence), pathologic (decay), and physical (mechanical damage) factors. In addition, contamination of fresh produce with foodborne human pathogens has become a concern. Gaseous ozone has multiple benefits including destruction of ethylene, inactivation of foodborne and spoilage microorganisms, and degradation of chemical residues. This article reviews the beneficial effects of gaseous ozone, its influence on quality and biochemical changes, foodborne human pathogens, and spoilage microorganisms, and discusses research needs with an emphasis on fruits. Ozone may induce synthesis of a number of antioxidants and bioactive compounds by activating secondary metabolisms involving a wide range of enzymes. Disparities exist in the literature regarding the impact of gaseous ozone on quality and physiological processes of fresh produce, such as weight loss, ascorbic acid, and fruit ripening. The disparities are complicated by incomplete reporting of the necessary information, such as relative humidity and temperatures at which ozone measurement and treatment were performed, which is needed for accurate comparison of results among studies. In order to fully realize the benefits of gaseous ozone, research is needed to evaluate the molecular mechanisms of gaseous ozone in inhibiting ripening, influence of relative humidity on the antimicrobial efficacy, interaction between ozone and the cuticle of fresh produce, ozone signaling pathways in the cells and tissues, and so forth. Possible adverse effects of gaseous ozone on quality of fresh produce also need to be carefully evaluated for the purpose of enhancing microbial and chemical safety of fresh produce.

Application of Processing and Packaging Hurdles for Fresh-Cut Fruits and Vegetables Preservation

Recently, consumers’ demand for fresh, nutritious, and convenient food has shown a significant rise. This trend has forced increased sales of minimally processed and/or pre-packed fruit- and vegetable-based products. New product development and the diversification of plant-based foods have supported this growth. The food production sector should balance this requirement with the necessity to provide safe food with extended shelf life while meeting consumer demands for novel, nutritious, and affordable food products. The use of alternative “soft hurdles” may result in a decrease in the rate of food deterioration and spoilage attributed to microbial activity or other physiological/chemical degradation reactions. The objective of the article is to provide a systematic review of the preservative effect of the available hurdles implemented during processing and packaging of fresh-cut fruits and vegetables, focusing on recent applications aiming at improving product quality and prolonging their limited shelf life.