Sanitary dips with calcium propionate, calcium chloride, or a calcium amino acid chelate maintain quality and shelf stability of fresh-cut honeydew chunks

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Abstract

Freshly cut honeydew chunks were dipped for 30 s in a solution containing 1.9 mM hypochlorous acid (ClO) without or with a 40 mM concentration of calcium (Ca) propionate, Ca amino acid chelate formulation (Ca chelate), calcium chloride (CaCl2), or not treated. Respiration and ethylene production rates, firmness, translucency, microbiological and sensory characteristics, surface color, volatile abundance, and tissue calcium content were evaluated during 7 d at 10 °C. Nontreated samples developed the highest respiration and ethylene production rates during storage, followed by samples dipped in ClO, ClO+CaCl2 or ClO+Ca chelate, and ClO+Ca propionate. Calcium salt and chelate treatments more than doubled tissue Ca content and inhibited changes in melon firmness, surface color, and the development of tissue translucency during storage. Treatment with ClO alone increased tissue translucency development, but inhibited surface microbial development. Microbial development was higher on nontreated melon samples than on ClO+Ca propionate-treated samples. Total quality-associated volatile abundance increased throughout storage and was higher in ClO+Ca propionate-treated samples than in other treated and nontreated samples. No sensorial preference was observed by consumer panels among ClO-, ClO+Ca propionate-, or ClO+Ca chelate-treated samples. The results indicate that a sanitary dip with Ca is a better alternative to a sanitary dip alone for quality maintenance and shelf-life stability of fresh-cut honeydew melon tissue.

Introduction

Fresh-cut honeydew melons (Cucumis melo L. (Inodorus Group)) are a common component of fresh-cut fruit products and are available year-round throughout the United States. Quality maintenance and shelf-life extension of fresh-cut products are important to the industry because of their economic impact. Honeydew melons are climacteric fruit with high respiration (Pratt et al., 1977) and ethylene production rates (Miccolis and Saltveit, 1991, Pratt et al., 1977), particularly among the widely grown hybrids (Kevin Crosby, personal communication), that make the fresh-cut products highly perishable, especially when temperature is not strictly controlled. Fresh-cut honeydew has a retail shelf-life of 2–5 d in air (Qi et al., 1999), less than half that desired in the distribution chain (Anonymous, 1996). In retail stores, the temperature fluctuates widely and often reaches 10 °C or higher (Lamikaura et al., 2000, Qi et al., 1999). Since the respiration rate of fresh-cut honeydew products at least doubles for every 5 °C increase above 5 °C (Watada et al., 1996), temperature management is essential for shelf-life extension.

In addition to good temperature management, fresh-cut melon shelf-life also may be extended by using modified atmospheres (Ayhan et al., 1998, Nguyen-the and Carlin, 1994, O'Conner-Shaw et al., 1996, Portela and Cantwell, 1998, Qi et al., 1999), strict sanitation to produce a sterile product (O'Conner-Shaw et al., 1996), or postprocessing with CaCl2 (Luna-Guzmán et al., 1999) or Ca lactate (Luna-Guzmán and Barrett, 2000) dips. Calcium salts, particularly CaCl2, have long been used as firming agents for canned fruits and vegetables (Camire et al., 1994). Calcium treatments also maintain firmness in a wide variety of whole, peeled, and fresh-cut fruits and vegetables including whole honeydew melons (Lester and Grusak, 1999) and fresh-cut muskmelons (Luna-Guzmán et al., 1999, Luna-Guzmán and Barrett, 2000). Calcium is reported to maintain firmness by crosslinking with cell wall and middle lamella pectins (Grant et al., 1973), stabilizing cell membranes (Picchioni et al., 1996), and/or affecting cell turgor potential (Mignani et al., 1995).

Calcium chloride can cause a bitter aftertaste in foods, including muskmelon pieces, while a similar Ca lactate treatment does not (Luna-Guzmán and Barrett, 2000). However, suprathreshold concentrations (1–100 mM) of Ca lactate solutions are slightly more sour than equimolar CaCl2 solutions, and both salts have an unpleasant taste (Tordoff, 2001). What effect low concentrations of these salts have in foods is not known. Calcium lactate has been suggested as a potential alternative firming additive for use in fresh-cut fruits (Luna-Guzmán and Barrett, 2000). Calcium propionate and Ca amino acid chelate formulations represent additional Ca sources that have been used in the food and/or nutritional industries but whose potential for use in the fresh-cut industry has not been explored.

Calcium propionate and propionic acid, which forms when the pH is lowered from neutrality, are widely used antimicrobial food additives and are GRAS (generally regarded as safe) in the United States with an upper limit only in identified foods (Davidson and Juneja, 1990). In preliminary experiments, we found that Ca propionate solutions at concentrations between 30 and 50 mM (<1% w/w) had no detectable flavor or lip feel and could be used with chlorinated water as a sanitary treatment for fresh-cut melon.

Calcium amino acid chelate formulations are patented as nutritionally functional chelates for plant, animal, and human use (Albion Laboratories, personal communication). A postharvest dip in a Ca amino acid chelate maintained firmness and more than doubled the shelf-life of intact honeydew fruit (Lester and Grusak, 1999). While more expensive than Ca salts, the Ca chelates are not corrosive to processing equipment and are more likely to penetrate deeply in plant tissues owing, at least in part, to their slow dissociation rate in water which would inhibit Ca binding to anionic cell wall sites within plant tissues. All of Albion's Ca chelate formulations have FDA GRAS status and all included ingredients have been certified Kosher and Parve by KOF-K Kosher Supervision of Teaneck, NJ (Albion, 1998). In preliminary experiments, we found that a formulation of Ca amino acid chelate for human use described as being taste free had a very limited solubility in water. Other formulations intended for human use and having a high solubility in chlorinated water had a proteinaceous odor as the dry powder, but were without a detectable odor or taste in solutions containing 40 mM Ca (percent dry mass variable depending on Ca content of the formulations).

Our objective was to determine the effects of just cutting or treating freshly cut honeydew chunks with hypochlorous acid (ClO)-containing water without or with Ca propionate, a highly water soluble Ca chelate formulation for human use, or CaCl2 on the quality of fresh-cut honeydew stored at 10 °C. The 10 °C temperature was used to simulate the abusive temperature that commonly occurs at retail stores and to accentuate any beneficial or negative effects of the postharvest treatments. Addition of ClO to the Ca solutions was evaluated to determine if chlorinated water with Ca supplements could be used to maintain quality and shelf stability of fresh-cut honeydew.

Section snippets

Fruit

Honeydew melons of unknown cultivar were obtained from the Maryland Wholesale Distribution Center in Jessup, Maryland. Only fruit containing at least 9% soluble solids content (SSC) were selected for these studies, with a range of <2% SSC within an experiment. The average weight of each melon was ∼2300 g. After overnight storage at 10 °C, 18 melons, free of defects, were selected visually for similarity of maturity and size, washed with 19 mM hypochlorous acid (1000 μl l−1 ClO supplied as sodium

Calcium levels

All of the Ca treatments similarly increased the Ca level in the samples by more than twofold (Table 1), the exact increase being dependent upon the Ca level in the tissue before treatment (data not shown). The Ca level at chunk surfaces was not measured, but was probably much higher in Ca-treated tissue than that for the tissue as a whole. While there was no significant difference in Ca levels between nontreated and ClO-treated tissue, the ClO-treated tissue consistently had a slightly lower

Acknowledgements

The authors wish to thank Michele Auldridge, Prayoon Charoennun, Willard Douglas, and Eun-hee Park for dedicated technical help. Use of a company name or product by the US Department of Agriculture does not imply approval or recommendation of the product to the exclusion of others that also may be suitable. The cost of publishing this paper was defrayed in part by the payment of page charges. Therefore, under postal regulations, this paper must be marked ‘advertisement’ solely to indicate this

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