| dc.description.abstract | Concealed Damage (CD), as defined by the almond industry, is a dark discoloration of the
almond kernel that occurs after heat exposure such as drying or roasting. CD is thought to be
associated with the Maillard reaction. The development of bitter flavors and a dark discoloration
can result in immediate consumer rejection. Although little is known about the chemical changes
that accompany CD, this type of damage may also influence other quality attributes such as shelf-
life. Investigating the conditions leading to the development of CD and the corresponding chemical
changes that occur is critical for improving almond quality. Postharvest moisture exposure (e.g.
rain) is known to increase the incidence of CD in raw almonds. Accordingly, the effect of moisture
exposure (6%, 8% and 11%) and temperature (35°C and 45°C) on the development of CD were
determined in raw almonds (variety Nonpareil). CD was monitored using colorimetry and by
measuring volatile organic profiles using HS-SPME-GC. Results indicate that although the
profiles of volatiles are similar between CD and NCD almonds, levels of volatiles related to lipid
peroxidation and amino acid degradation are higher in the CD group. Importantly, we found that
moisture exposure resulting in a kernel moisture content at or above 8% is a key factor in the
development of CD and that temperature increase is a factor in the development of CD. Almonds with CD do not present any visible defect before heat treatment and there are no
screening methods available to identify CD in raw almonds. In fact, the most common method for detecting almonds with CD involve visual inspection of roasted almonds. Visual inspection is time
consuming, labor intensive and cannot be used to detect CD in almonds before roasting. To address
this, NIR spectroscopy was investigated for the detection of CD in raw almonds. NIR was
evaluated as it is a non-destructive method and suitable for in-line sorting of raw almonds. Using
partial least square regression and discriminant analysis (PLS-DA), data pre-processing (SNV and
second derivative), and selected wavelengths, a predictive method was developed. This model
based upon measuring four wavelength ranges (i.e.1408–1462, 1692–1740, 1902–1959 and 2064-
2104 nm) corresponding to lipids, carbohydrates and protein. We demonstrate that NIR
spectroscopy can be used to monitor the degradation of lipids, carbohydrates and proteins in
almonds with CD with an error rate of 8.2%. Our model is a significant improvement over
previously reported NIR approaches with error rates ranging from 5.8 – 27.5%.
Under current commercial practices, almonds are dried in the field to a moisture content of
~6%. However, during wet seasons when the almonds cannot be dried in field, they are brought to
the processors to be dried. To date, there are no time/temperature guidelines for drying almonds
other than the targeted ~6% moisture. Herein, the effect of drying moisture exposed almonds at
temperatures ranging between 45°C– 95°C, prior to roasting, was evaluated on the impact of CD.
Amadori compounds, reducing sugars and headspace volatiles (HS-SPME-GC/MS) were
evaluated. Results indicate that drying temperatures between 45°C - 65°C decrease visible signs
of CD up to 40%; while, drying temperatures above 75°C increases visible CD up to 100%. No
significant differences were found for reducing sugar, and Amadori compounds among the
different drying conditions. The volatile profile was characterized by increases in compounds
related with lipid oxidation which increased with drying temperature. Increases in lipid oxidation
by-products may result in reduced stability of almonds during storage and promote early rancidity development. Herein, moisture exposed almonds dried at 55°C and 75°C were stored under
accelerated shelf-life conditions (45°C/80%RH) for 4 weeks and evaluated for headspace volatiles.
The volatile profile of almonds dried at 55°C were not significant different from control almonds.
Our results demonstrate that raw almonds that have been exposed to moisture and then dried at
55°C reduce volatiles related to lipid oxidation during accelerated storage. Furthermore, our results
suggest that lipid oxidation by-products are key precursors for browning reaction and that reducing
sugars play only a minor role in browning related to CD. | |
