![]() Proper use of hurdles can appreciably lengthen shelf life of unpasteurized juices without unduly affecting quality. yeast, lactic acid bacteria, etc.) Antimicrobial substances, either natural or chemical preservatives, also assist. (Although anaerobic conditions are dangerous with low acid foods and can even set the stage in high acid products for anaerobic spoilage organisms, i.e. The exclusion of oxygen is an additional barrier. Fortunately most juices are acid, or amenable to acidification. An acid environment of pH less than 4.5 (ideally less than 3.5) restricts the growth of many organisms. Thus good sanitation is the first barrier to reduce microbial load low storage temperature further retards growth. The hurdle principle is based on the premise that while any single barrier to microbial growth may be inadequate for desired protection, a number of barriers together can enhance product stability (Figure 8.1). In circumstances where thermal processing is impractical, minimal processing employing hurdles is called for. The thawed juice then has a shelf life limited by sanitary conditions and pre-freezing treatments. "Fresh frozen" is the appropriate designation. Although the product cannot be labelled as such, subsequent thawing and proper packaging approximate fresh juice. For frozen products, the closer to thawing temperature they become, the faster these reactions occur. Slow deterioration (over months) is exhibited by decline in nutrients, primarily loss of ascorbic acid, enzymatic activity as well as flavour, colour and viscosity changes. However, it is a costly alternative and appropriate only where product value merits freezing and holding large volumes of single strength juice. Single strength juice freezing and storage in a low oxygen environment can maintain fresh character as well or better than any other process. Thus low temperature during manufacture and storage is a valuable hurdle to deterioration. 8.1.2 FreezingĪll preservation methods that allow juice storage above refrigeration temperatures, greater than about 5✬, are limited by Maillard browning and other slow but persistent reactions. The resulting scorched flavour and colour does not do justice to the fruit so treated, easily reduces consumer appeal and destroys market potential. A major quality defect in pasteurized tropical juices and juice beverages is over heating or holding the product at too high a temperature before or after pasteurization. However, there are someĭelicate-flavoured juices, most of tropical origin, that cannot tolerate even the most gentle pasteurization step. With many juices heat is tolerableĪnd commercially acceptable packs are available. Reactions change the character of the juice. Thermal processing does away with theĪbsolute need for refrigeration and inactivates enzymes. Then the juice cannot be labelled "fresh". Packaging can further increase storage life with minimum quality changes, but Refrigeration combined with pasteurization and hermetic One rule of thumb specifies each 10✬ increase in temperature roughly doubles reaction rates. Going from an exceptionally low refrigeration temperature to a merely good one (2✬ to 5✬) can reduce shelf life from greater than a month to less than 3 weeks. Several accompanying difficulties are the possibility of other quality-reducing reactions comprising enzymatic, oxidative and the challenge of maintaining minimum refrigeration temperature throughout distribution, including in the consumer's refrigerator. A holding temperature as close to the juice freezing point as possible (-1 to -3✬, depending on soluble solids), combined with efficient preparation and exceptional sanitation in preparation and packaging can extend storage life up to a month. Microbial load can be appreciably reduced by good handling and sanitary practices, but not eliminated. Microbes, the natural microflora present will be active. Two practical "processes" capable of extending storageĪre rigorous attention to good sanitation from production through juice As indicated, this is a very transitory product having a limited shelf life of hours or days even under the best of circumstances. In general, the fresher the juice, the higher the quality, so the standard of excellence is often freshly prepared, unprocessed juice (Sizer and Balasubramanian, 1999 ). A principle tenant of food preservation is to maintain the quality and nutritional attributes while preventing spoilage. Principles and practices of small - and medium - scale fruit juice processingĬHAPTER 8 JUICE STABILIZATION AND PRESERVATION 8.1 Preservationĭespite the many pathways to deterioration, there are a number of effective preservation methods that have evolved to combat spoilage. ![]()
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