ReviewCalcium for extending the shelf life of fresh whole and minimally processed fruits and vegetables: a review
Introduction
Fruit and vegetable consumption is growing rapidly in recent years. Associated with the new consumer's profile “rich in cash/poor in time”, there is a demand for ready-to-eat products. For this reason, the market of minimally processed fruits and vegetables has grown rapidly in recent decades as a result of changes in consumer attitudes (An Bord Glas, 2002). Leafy vegetables in particular are a rich source of antioxidants such as beta-carotene and ascorbic acid (Arthey and Dennis, 1992, Negi and Roy, 2000). Also, the link between the consumption of these products and the lower risk of suffering certain chronic diseases (Ruowei et al., 2000, Subar et al., 1995) has been contributed to the consumer's attitude change during recent decades.
Minimally processed vegetables, also called ready-to-use, fresh-cut or pre-cut produce, are raw fruits and vegetables that have been washed, peeled, sliced, chopped or shredded prior to being packaged for consumption (Barry-Ryan & O'Beirne, 1998). They are also defined as those subjected to some processing techniques of lesser magnitude than canning or freezing but which, nevertheless, add value to the product before distribution and consumption (King & Bolin, 1989). The marketing of minimally processed fruits and vegetables is limited by a short shelf life and rapid deterioration of their components due to tissue damage as a result of processing, e.g. washing or cutting, and the microbial growth (Watada & Qui, 1999). In recent years, the use of physiologically active compounds (PAC) has attracted interest of consumers and the industry (minerals, probiotics, etc.) (Alzamora et al., 2005).
Titchenal and Dobbs (in press) point out some dark green leafy cabbage family vegetables and turnip greens as good calcium sources, and most leafy vegetables as potential calcium sources. The major source of calcium in the United States diet is dairy products, which supply 75% of the intake, and vegetables, fruits and grains which supply the rest (Allen, 1982).
The awareness of consumers on the benefits of calcium is relatively high. The calcium content in the diet is critical in most stages of life (Gras, Vidal, Betoret, Chiralt, & Fito, 2003). Dietary calcium raises concern for consumers and health specialists due to the number of processes it is involved in, the high amount present in the body, and the continuous research highlighting the benefits of an adequate intake. Nowadays, an increasing part of the products in the food industry are fortified, especially dairy products followed by beverages and snacks (Caceres, Garcia, & Selgas, 2006). The interest in calcium has intensified in recent years as a result of evidences linking osteoporosis, hypertension and cancer to calcium deficiency. While the cause of these diseases is multifactor and poorly understood, there is some evidence to support the hypothesis that increased calcium intake might reduce the risk of suffering from these diseases (Appel et al., 1997, Cumming et al., 1997). Also, the use of phosphorous-free sources of calcium, such as gluconate, citrate, lactate, acetate and carbonate calcium salts, can help to obtain a good balance of calcium and phosphorous in the diet (Cerklewski, 2005). To give consumers the opportunity to increase their calcium intake without resorting to supplementation, the industry has been encouraged to fortify food and beverages with calcium (Cerklewski, 2005). This opens new ways of supplementing calcium intake by increasing the calcium content in these commodities. For this reason, the use of natural sources of calcium as preservative with a nutritional fortification effect presents an advantage for the industry and for the consumer.
Section snippets
Calcium sources to maintain the shelf life of fresh vegetables and fruits
Different calcium salts have been studied for decay prevention, sanitation and nutritional enrichment of fresh fruits and vegetables. Calcium carbonate and calcium citrate are the main calcium salts added to foods in order to enhance the nutritional value (Brant, 2002). Other forms of calcium used in the food industry are calcium lactate, calcium chloride, calcium phosphate, calcium propionate and calcium gluconate, which are used more when the objective is the preservation and/or the
Methods for calcium application on fresh-like minimally processed fruits and vegetables
Two main ways of application of the calcium in fresh fruits and vegetables have been reported: dipping–washing (I) and impregnation (II) processes.
(I) Dipping treatments are commonly used for fresh products, especially those more perishable, such as leafy vegetables. It usually consists of the soaking of the product, applying or not applying mechanical agitation, followed by the removal of excess washing solution. This treatment is gentler to the product than the impregnation techniques which
Effect of calcium treatments on the commodities: quality, safety and nutritional issues
Calcium is involved in maintaining the textural quality of produce since calcium ions form cross-links or bridges between free carboxyl groups of the pectin chains, resulting in strengthening of the cell wall (Garcia et al., 1996). Calcium complexes to cell wall and middle lamella polygalacturonic acid residues, improving structural integrity (Van-Buren, 1979).
Manganaris et al. (2007) suggested 62.5 mM calcium chloride immersion treatment as a potential postharvest treatment for whole peaches,
Importance of calcium in the industry: cost and benefits
Today's consumer has, on average, a busier lifestyle than in previous decades. Income, as measured by Gross National Product (GNP), has been rising over the past two decades, throughout the EU and the US. Both unemployment and interest rates have generally been declining throughout the 1990s, substantially increasing consumer's disposable income. This means that consumers have the ability to spend more on higher value or added-value foods, even though the current percentage spent on food from
Future research needs
From the point of view of the possibilities in the fortified food market, there is a wide range of opportunities to develop new products using calcium treatments, due to the high and increasing demand of fresh and healthy food. When using impregnation techniques, the behaviour of the vegetable or fruit matrices is highly produce-specific, increasing the amount of research needed. Also, some issues regarding impregnation techniques, especially vacuum impregnation need further research.
Acknowledgements
This research was supported by a Technological Sector Research Grant (2002–2006) and International Collaboration Award Scheme (ICAS) (2005–2007). Authors acknowledge Elsevier publications for the permission to reproduce parts of figures and tables for this review.
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