Application of Color Sorting Technology for Reduction of Fruity Fermented Off-flavor and Improvement of Flavor and Shelf Life of Roasted Peanuts

Abstract

A range of maturity stages is present in peanut pods at any harvest date due to an indeterminate flowering habit. Since the size-maturity relationship is not absolute, immature peanuts are found in all grade sizes. Immature peanuts are associated with increased fruity fermented off-flavor potential at high curing temperatures (>35 degrees C). Upon roasting immature peanuts acquire a darker roast color and have lower roast peanutty flavor than mature peanuts. The objective of this study was to determine the effectiveness of a novel application of machine color sorting for reduction of fruity fermented off-flavor and improvement of flavor and shelf life of roasted peanuts. Two fruity-fermented peanut lots of Flavor Runner 458 from the years 2002 and 2003 and a non-fruity fermented lot of Georgia Green (65 kg each) were roasted to a target Hunter L value of 49 ± 1, blanched, and subdivided into 3 sub-lots. Each sub-lot was color sorted using a Sortex color sorter. The sensitivity parameter of the color sorter was increasingly adjusted to separate about 5, 20 and 30 % of the darkest peanuts (rejects) from the lighter ones (accepts). Hunter L values of 40 ± 2, 43 ± 2 and 45 ± 2 were recorded for the first, second and third reject fractions (dark peanuts) respectively for all peanut lots. All rejects had lower Hunter L values than the corresponding accept fractions by 8 ± 2 units.

A panel highly trained in peanut flavor descriptive sensory analysis evaluated the unsorted and color sorted fractions for all flavor attributes. Statistical analysis indicated significant differences among the light and dark color-sorted peanuts (p <0.0001). The third accept (2002 and 2003 fruity fermented crops) formed after removing ca. 30 % dark peanuts had the highest roast peanutty intensity (4.63 and 4.69). The first reject (2003) consisting of 6.6 % of darkest peanuts received the lowest score for roast peanutty (3.7) and the highest score for fruity off-flavor (3.1). In both the 2002 and 2003 lots there was a reduction in the intensity of fruity fermented off flavor from 2.4 and 2.76 respectively in the unsorted peanuts to 0.48 and 0.41 respectively in the third accept. Dark roast flavor and bitter taste decreased significantly (p> 0.0001) with removal of higher percentage of dark peanuts in the fruity-fermented 2003 crop. No significant differences were established in the descriptive flavor analysis among the accept fractions in the non-fruity fermented lot. Results from chemical analysis demonstrated that the first reject with ca.5 % of darkest peanuts had significantly lower percentage of oil content (45-46%), higher free fatty acid values (0.22-0.26) and lower O/L ratio (11.48-11.58) in the fruity fermented lots. The rejects from the non-fruity fermented lot had significantly lower O/L ratio (1.54-1.60), higher free fatty acid value (2.45-2.58) and higher sugar concentration (75-82 mg/g). No significant differences were established in the shelf life characteristics among the accept fractions in all peanut lots.

The results indicated that fruity fermented off-flavor decreased with the removal of successively higher percentage of darker-roasted immature peanuts. This technology provides a method of remediation of peanuts, which have the fruity fermented off-flavor.