The effects of post-harvest treatments on the quantity and quality of ready-to-eat fresh vegetables during the storage period

Dissertation for receiving a master's degree in the field of food science and engineering

Trend: food science and industry

Abstract

Given the various uses of vegetables in human nutrition and also because of their taste and usefulness in maintaining health and Their health is increasing day by day. Considering the short life after harvesting and microbial contamination of vegetables, the need for research in this field seems necessary. In this study, the possibility of increasing the shelf life and reducing the microbial load of two commonly used edible vegetables, mint and watercress, was evaluated by using salicylic acid (0, 0.5 and 1 mM), calcium chloride (0, 1 and 2%) and plant essential oil (0,500 and 1000 ppm). The experiment was conducted as a factorial in the form of a randomized complete block design with 7 treatments and two maintenance periods in three replications. The results showed that by increasing the storage period in both vegetables from three days to six days, the rate of spoilage, leakage of electrolytes, proline and relative humidity content increased and the amount of chlorophyll decreased. Among the treatments used, salicylic acid and calcium chloride increased the shelf life of both vegetables, so that these substances decreased the apparent index of spoilage and leakage of electrolytes, and increased the content of relative humidity and the amount of chlorophyll. Concentrations of 0.5 millimolar salicylic acid and 1% calcium chloride were more effective. Based on the obtained results, only the use of plant essential oil significantly reduced the microbial load in vegetables, and other treatments were not effective on this feature. In general, salicylic acid and calcium chloride can be recommended to increase the shelf life of vegetables during the storage period and plant essential oil to reduce the microbial load of the studied vegetables. rtl;">

- Introduction

    Fresh fruits and vegetables are essential components of the human diet and there are significant evidences of their health and nutritional benefits. Consumers expect fresh and processed fruits and vegetables to have a long shelf life in addition to high nutritional and organoleptic quality (Abdias et al., 2008)[1]. From cultivation to the shelf, every stage in which the product is placed is important in terms of quality and safety. The quality of fresh fruits and vegetables is a combination of features including appearance, texture, taste, nutritional value and safety. The quality of ready-to-eat fruits and vegetables depends on pre-harvest agricultural operations (genotype, weather conditions, cultivation operations), ripening (ripening and ripening) and post-harvest factors (physical damage during harvesting and handling, temperature and relative humidity management, complementary processes applied to the product, complementary processes by changing the product atmosphere and harvesting method). A proper quality assurance program should address all of these factors affecting the quality of healthy fruits and vegetables and their fresh-cut products. Low-processed vegetables[2] refer to ready-to-eat products[3] or fresh cut products[4]. In fact, vegetables and fruits are raw, which are washed and peeled and sliced, chopped or grated before packaging for the consumer (Ayala-Zavala et al., 2008)[5]. Also, these low-processed products refer to cases where the processes performed on the product are not like the process of canning or freezing, but in any case, it increases the value of the product before distribution (Vipul Gohel, 2006) [6]. Fresh cut product production operations, especially cutting and peeling, increase respiration and ethylene production, intensify water loss, stimulate the accumulation of secondary metabolites, cell decomposition and enzymatic browning. Also, tissue damage may cause microbial growth and ultimately product spoilage. Microbial growth in tissues is influenced by the chemical composition of the tissue. The safety technology of fresh cut products must control pathogenic and spoilage microorganisms and at the same time prevent severe processes and reduce tissue growth and viability. These methods are based on the use of a series of hurdles.

Bacterial contamination with Listeria monocytogenes, Salmonella and Escherichia coli of ready-to-eat fresh vegetables can occur at different stages of growth, during harvesting, post-harvest processes or during handling. The prevalence of diseases caused by fruits and vegetables has increased significantly in recent years (Abadias, 2008) [7]. Adding disinfectants to wash water can significantly reduce the population of plankton bacteria cells and thus reduce the risk of secondary contamination. Such a reduction improves the safety and durability of the product, as a result, workshops and packaging factories of ready-to-eat fresh vegetables can increase the shelf life of the product by disinfecting and disinfecting, and as a result, they can make it easier for consumers to consume fresh vegetables. The amount of reduction of pathogenic microorganisms during the washing and disinfection process is not enough to guarantee the quality of the food (J. M. Sapers, 2009) [8]. The microbial, sensory and nutritional shelf life of processed vegetables and fruits should be at least 4-7 days (Veliz Raiura, 2005) [9]. Reducing yeasts and molds in processed and ready-to-eat vegetables is necessary to improve the quality of the final product and increase its shelf life (J.D. Hillgreen et al., 2000) [10]. Washing vegetables with water reduces the natural microbial flora by approximately 1 logarithmic unit. Therefore, there is a need for antimicrobial compounds to reduce the microbial load in washing water systems. Several studies have shown that chlorine used in concentrations allowed by the FDA[11] is not effective enough to remove human pathogens and spoilage microorganisms. In addition, it may combine with organic matter in water and create mutagenic compounds. Alternatives to chlorine such as chlorine dioxide, acidified sodium chlorite, peroxyacetic acid and some essential oils have recently been suggested (Yosefizad et al., 2012, Suel Ruiz [12], 2012). Prasidine 15% [13] has no mutagenic effect and has been approved by the FDA as a vegetable and fruit disinfectant. The most biocidal compound in the world is peracetic acid. It has an official license of up to 500 ppm on surfaces in contact with food and is an effective disinfectant against all microorganisms. Unlike chlorine, it has no harmful residues and preserves the quality, nutritional value and vitamins of vegetables. Its antimicrobial function is basically related to the production of active oxygen species that cause damage to DNA, breaking the cell membrane and blocking enzymes (Yosefizad et al., 2013). The total number of bacteria in fresh vegetables depends on the type of bacteria and the existing conditions and usually varies from 102 to 107 per gram. (William Frazier[14] et al., 1379).

The desire of consumers to use natural products free of any unsafe chemical processes and preservatives has caused manufacturers to search for safer processes to increase the shelf life of ready-to-use cut products. Non-volatile compounds such as plant essential oils have been considered due to being GRAS[15]. Studies have shown that many essential oils They have antimicrobial properties, among which the essential oil of bay leaves, sweet pepper, coriander, black cumin, cardamom, fennel, parsley, mustard, mint, dill, cloves, oregano, rosemary, thyme, sage and vanilla can be mentioned. Active compounds in essential oils often have a broad antimicrobial spectrum against pathogenic microbes of food origin and spoilage bacteria. Of course, many of these essential oils are effective against a specific microbial species. . Major volatile compounds with antimicrobial activity and flavoring of essential oils include isoprenoids, organic sulfur, aldehydes, and alcohols. Antimicrobial activity of essential oils is due to their chemical structure and especially the presence of hydrophilic functional groups such as hydroxyl groups of phenolic compounds or lipophilic of some essential oils (Losera et al., 2012)[16].

Due to the adverse effect of chemical preservatives used in food products on human health, essential oils have been proposed as safe compounds to increase the shelf life of fresh fruits and vegetables.