Effectiveness Of Sorting And Sorting Methods

That removal of damaged and decayed fruit and vegetables prior to storage or subsequent processing should reduce microbial loads and thus reduce any risk of foodborne illness would seem intuitive. However, data to document the actual level of reductions achieved by sorting and culling are not always available. In data provided by the Florida Department of Citrus, juice microflora was 4.5±0.7logCFU/ml with no grading, 3.7± 1.0logCFU/ml with light grading, and 2.2 ± 0.6 log CFU/ml with moderate grading [10]. Light grading was defined as splits removed, 0.5 to 1% of fruit stream; and moderate grading was splits, peel plugs, and significant blemishes removed, 2 to 3% of incoming fruit stream.

Sorting and removing poor-quality apples during cider production results in a reduction in aerobic counts in the final cider. In one recent study, cider was produced from seven different apple varieties. Production variables included method of harvest, quality sorting, and storage. Cider from fresh ground-harvested fruit, considered to be lowest quality and greatest risk, had significantly greater numbers of aerobic microflora (4.89 log CFU/ml) than any cider from tree-harvested fruit (Figure 16.1) [11]. Yeast and mold populations were also elevated in ground-harvested fruit (Figure 16.2). Cider from unsorted and unculled fruit had an average of 3.45 log CFU/ml, whereas cider from sorted and culled apples had an average of 2.88 log CFU/ml (p < 0.05) [11]. As with ground-harvested fruit, yeast and mold populations were elevated in cider from apples that were not sorted and culled prior to cider production.

Along with the examination of microflora levels in sorted or unsorted apples, the cider in the same study was also tested for changes in the level of patulin [12]. Patulin levels varied depending on storage and variety. No patulin was detected in cider produced from any fresh tree-harvested fruit. However,

Harvest FTC FTU FGU STC STU FTC FTU FGU STC STU conditions Apple Cider

FIGURE 16.1 Differences in Tukey box plots of aerobic plate counts (APC) of pooled apple varieties due to harvest conditions, storage, and culling. Means sharing a letter were not statistically different at the p < 0.05 level. FTC = fresh, tree-harvested, culled; FTU = fresh, tree-harvested, unculled; FGU = fresh, ground-harvested, unculled; STC = stored, tree-harvested, culled; STU = stored, tree-harvested, unculled. (Modified from Keller, S.E. et al, J. Food Prot, 67, 2240, 2004. With permission.)

Harvest FTC FTU FGU STC STU FTC FTU FGU STC STU conditions Apple Cider

FIGURE 16.1 Differences in Tukey box plots of aerobic plate counts (APC) of pooled apple varieties due to harvest conditions, storage, and culling. Means sharing a letter were not statistically different at the p < 0.05 level. FTC = fresh, tree-harvested, culled; FTU = fresh, tree-harvested, unculled; FGU = fresh, ground-harvested, unculled; STC = stored, tree-harvested, culled; STU = stored, tree-harvested, unculled. (Modified from Keller, S.E. et al, J. Food Prot, 67, 2240, 2004. With permission.)

Harvest FTC FTU FGU STC STU FTC FTU FGU STC STU conditions Apple Cider

FIGURE 16.2 Differences in Tukey box plots of yeast and mold populations in pooled apple varieties due to harvest conditions, storage, and culling. Means sharing a letter were not statistically different at the p < 0.05 level. FTC = fresh, tree-harvested, culled; FTU = fresh, tree-harvested, unculled; FGU = fresh, ground-harvested, unculled; STC = stored, tree-harvested, culled; STU = stored, tree-harvested, unculled. (Modified from Keller, S.E. et al, J. Food Prot., 67, 2240, 2004. With permission.)

Harvest FTC FTU FGU STC STU FTC FTU FGU STC STU conditions Apple Cider

FIGURE 16.2 Differences in Tukey box plots of yeast and mold populations in pooled apple varieties due to harvest conditions, storage, and culling. Means sharing a letter were not statistically different at the p < 0.05 level. FTC = fresh, tree-harvested, culled; FTU = fresh, tree-harvested, unculled; FGU = fresh, ground-harvested, unculled; STC = stored, tree-harvested, culled; STU = stored, tree-harvested, unculled. (Modified from Keller, S.E. et al, J. Food Prot., 67, 2240, 2004. With permission.)

cider pressed from controlled atmosphere (CA) stored apples did contain significant levels of patulin. These patulin levels were significantly reduced in most varieties when the apples were culled prior to cider production. Chapter 13 contains a more in-depth review of patulin in apple cider.

Sorting and culling are included in a 1999 survey of industry practices published by the USDA [13]. This report covers 30 fruit and vegetable commodities in 14 states. The report focuses on fruit and vegetable commodities that are predominately consumed raw, as these represent a substantially greater risk than produce that undergoes further processing. Of all the produce in the survey, the vast majority was harvested by hand. For fruit acres, 94% was harvested by hand only, whereas for vegetable acres, 87% was harvested by hand. The majority of packers in this survey manually sorted both fruit and vegetables. It should be noted, however, that produce in this survey was intended for the fresh (consumed raw) market, and for many specific types of produce in the survey, data were unavailable. Nonetheless, the survey reported that 100% of apples, table grapes, broccoli, celery, cucumbers, cantaloupes, and honeydew melons were manually sorted.

That manual sorting and culling are used for the majority of fresh produce is not surprising. Mechanical handling and sorting can result in substantial damage, increased losses, and may incur considerable expense to implement.

In a study on grade-lowering defects in grapefruit, mechanical injury levels were found to increase from pregrading areas (5.6%) to final grading (8.6%) and to final packaging (12.3%) [14]. Increased injury was also related to increased levels of bacterial soft rot in Bell peppers [15].

Despite such reported problems, mechanical handling and sorting have an advantage in speed. For manual sorting, fruit or vegetables are sorted either in the field or at the packinghouse. Most frequently, a sorting table and/or conveyor are used. Care must be taken that the speed of the conveyor is slow enough to allow individual examination by personnel of each piece. Most mechanical systems consist of two basic elements, a conveyor and some means of separation, based on specific fruit or vegetable characteristics such as size, weight, color, and/or the presence of defects. The simplest of such instruments sorts using uniformity of size and shape by means of appropriate holes or sizers. Such simple sorting machines still require considerable worker attention, but can significantly increase sorting speed, particularly for less fragile produce. Such instruments would not, however, detect other defects.

More elaborate and modern instruments that sort by color and defects using camera-based systems and computer technology are available commercially. Produce is conveyed in traditional fashion to a scanning area where it is scanned and analyzed using computer programs to determine appropriate grade. Use of such a method was described by Leemans et al. for apples [16]. Leemans et al. reported correct classification up to 78% for Golden Delicious apples and 72% for Jonagold. Classification was based on external quality parameters such as color and texture.

Both manual sorting and machine sorting based on camera methods detect defects and characteristics external to the fruit or vegetable. However, some defects may be small and difficult to detect. Other defects may be internal and not detectable using any surface examination methods. More recently, research has been directed at the development of methods that may allow the detection of such internal defects in a nondestructive manner. These new methods are based primarily on X-ray imaging, magnetic resonance imaging (MRI), or near-infrared spectroscopy (NIR) spectroscopy [17-24].

Some produce types are not particularly suitable for machine sorting, frequently because of their fragile nature. For such produce, researchers look for novel means of assessing quality that may require less manual manipulation of the produce. One such method that has potential is the use of an electronic system that measures aromatic volatile gas emissions. Such a method was employed by Simon et al. to assess the quality of blueberries [25]. The method successfully detected differences in maturation levels and detected damaged fruit in closed containers of blueberries.

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