Freshcut Carrots

Fresh-cut carrots are distributed as slices, sticks, shreds (grated carrots), or bite-size pared products referred to as "baby" carrots. These are normally derived from the mature root, although specialty items prepared with immature plants grown for the purpose are available in the marketplace. The appearance of''white blush" on cut surfaces is a serious quality problem with all fresh-cut carrot products. The phenomenon is believed to result mainly from dehydration of the cut surface but enzymatic reactions leading to lignification may contribute to the phenomenon. Some processors dip carrot products in citric acid to delay enzymatic whitening, and most package the product without drying to avoid rapid dehydration of the surface. The use of proprietary humectants that prevent dehydration and preserve the appearance of freshly sliced carrots is also practiced.

Freshly harvested carrots carry microbial populations dominated by species derived from soil. In-field washing in chlorinated water to remove excess soil is a common practice, and the harvested crop is often stored prior to distribution and processing. In some jurisdictions, fungicides such as thiabendazole and/or iprodione (Rovral) and bactericides such as chlorane are applied for the control of storage disease [1]. Under ideal conditions storage temperature is held close to 0°C, and relative humidity is maintained above 90% to reduce respiration rates, limit weight loss, and discourage growth of microorganisms responsible for postharvest diseases. There is little doubt that postharvest treatments such as these alter the microflora of raw carrots destined for processing, although their influence on microorganisms of significance in fresh-cut products has not been examined in detail. Similarly, the processing plant is also expected to contribute spoilage microorganisms to the finished product. Unfortunately, the microbial ecology of the processing environment is poorly understood.

Microbiological examination of carrot sticks at various stages of processing has shown that peel is a major source of microbial contaminants on the finished product. A survey of processing establishments by Garg et al. [2] revealed that peeling reduced mean total aerobic populations from 6.5 x 106 to 3.6 x 104CFU/g. It should be noted that the samples analyzed for this work were prepared by blending cut pieces. Hence the actual population density on the peel of raw carrots may have been several orders of magnitude greater. The data derived from this study clearly showed that peeling results in the transfer of microorganisms from the outer epidermis of the raw material to surfaces exposed by cutting. It is also interesting to note that populations remained unchanged during slicing or dipping in a chlorinated water ice bath. Mean total aerobic populations on the finished product were in the range 104 to 105 CFU/g, in close agreement with a separate study by Odumeru et al. [3]. Garg et al. [2] found large populations of Gram-negative psychrotrophic bacteria, particularly Pseudomonas spp., lactic acid bacteria, and fungi on freshly prepared carrot sticks. The fate of these microorganisms during refrigerated storage was subject to the influence of preparation method, composition of the atmosphere in the package, and storage temperature. Izumi et al. [4] compared various quality attributes in carrot slices, sticks, and shreds stored in air or under controlled atmosphere (0.5% O2, 10% CO2). Although differences were not always statistically significant, total aerobic microbial populations were highest in shreds, followed by sticks and slices. Hence there appears to be a relationship between the degree of damage to plant tissues, available surface area for colonization, and the extent of microbial growth.

Rapid quality changes in commercially packaged, shredded carrots and the suspected involvement of microorganisms led to detailed microbiological examination of these products by Carlin et al. [5-7]. Most are distributed in impermeable films or rigid containers. Rapid depletion of oxygen to less than 2% and accumulation of carbon dioxide to more than 30% due to accelerated respiration in plant tissues leads to the establishment of atmospheres conducive to the growth of microaerophilic and facultatively anaerobic species. Lactic acid bacteria, particularly the heterofermentative species Leuconostoc mesenteroides, and yeasts quickly become the predominant groups, and both lactic acid and ethanol accumulate in the product [5]. Controlled atmospheres containing 15 to 20% CO2 and 5% O2 can delay these changes [6-7]. Kakiomenou et al. [8] also examined the influence of temperature and various modified atmospheres on these events. Lactic acid bacteria were always the dominant group, particularly at higher temperatures (10°C).

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