Minimally Processed Fruits and Vegetables

MP produce includes fresh fruits and vegetables that may be washed, chopped, trimmed, peeled, sliced, or shredded prior to packaging and storage at refrigeration temperatures. There is increasing consumer demand for MP produce, due to the level of convenience offered by pre-use processing and availability as a fresh RTE or RTU food. MP produce typically is not washed or cooked prior to ingestion, increasing the risk of food poisoning. Thus the level of quality and safety of MP produce must be quite high for the shelf life achieved. MAP has great potential as a strategy to achieve this goal, and much research and development effort has been initiated to develop useful MAP systems for a variety of MP produce.

Commercial MAP systems have been developed for a wide range of whole fruits and vegetables. However, these same systems cannot be used in parallel commodities that have been processed; processed produce deteriorates and metabolizes much differently from whole produce. Processing steps such as chopping, slicing, and dicing rupture tissues and cells, releasing nutrients and degradative enzymes such as oxidases. Plant cells are less physically resistant to microbial invasion, nutrients are made more available for microbial growth, respiration rates increase, and surface area increases, allowing for greater incidence of spoilage. Processing thus significantly reduces shelf life, producing a highly perishable product compared to whole fruits and vegetables; whole produce that may be stored for several weeks under refrigerated MAP storage when processed may only have a 1- to 2-day shelf life.

It is a challenge to create a MP produce commodity that exhibits high quality and safety over a reasonable amount of time for feasible distribution and sale. MAP technology has the potential to provide adequate shelf life for MP produce, particularly when used in combination with additional hurdle or control strategies. MAP strategies must be created for each specific commodity and preparation method, as commodity characteristics and indirect effects of preparation steps can influence package EMA, microbial growth, and shelf life. Allende and others [40] looked at microbial levels on commercial fresh processed red Lollo Rosso lettuce after reception and processing steps of shredding, washing, draining, rinsing, centrifugation, and packaging and found that shredding, rinsing, and centrifugation significantly increased bacterial counts. Improvements made to reduce microbial levels during each of these three steps resulted in further extensions to shelf life when the product was stored under MAP conditions. Others have found that some processing methods can increase the respiration activity of some produce commodities by 1.2- to 7-fold or more. Hand peeled carrots exhibited a 15% increase in respiration rate while machine peeled carrots exhibited a 100% increase in respiration rate; the respiration rate during storage also differed between the two processing methods [20]. Pretel and others [41] found significantly different respiration rates and mesophilic bacterial growth on MAP-stored enzymati-cally peeled versus manually separated oranges; manually separated oranges generally exhibited a higher level of bacterial growth and production of CO2 than enzymatically peeled oranges. These differences could be ameliorated to some extent by manipulating packaging film permeabilities and storage temperature, achieving similar shelf lives. MP fruits will pose different storage challenges from vegetables, due to differences in inherent composition, physiology, biochemistry, and microbiology as well as differences in processing procedures and equipment. Thus the MAP strategy must be matched to not only a particular commodity, and whether whole or processed, but also to the specific processing method.

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