UC Davis

This thesis assesses the quality of windfall almonds (Prunus dulcis (Mill.) D. A. Webb) in alignment with the goal of the California almond community to halve dust emissions during almond harvest by 2025. Windfall is the premature fall of almonds before harvest, usually due to varietal characteristics or weather conditions and mechanical knocking by machines passing through the orchard. One option is to transition to alternative off-ground harvest systems like catch-frames. The transition poses a potential unknown loss of marketable yield in the form of windfall that would not be picked up if the on-ground harvest is abandoned. Additionally, the windfall is a concern for current harvest systems since windfallen nuts that lie on the orchard floor for extended periods might disproportionately affect crop quality, food quality, and food safety of the resultant harvested nuts.The first chapter reviews the literature regarding current and future trends of almond production in California and almond quality parameters. The second chapter describes the quality of windfallen Nonpareil almond fruits as determined in the 2019 and 2020 seasons by incubating them on the ground at three maturity levels corresponding to 5% hull split (mid-July or T4 = 4 weeks pre-harvest until T0), 50% hull split (early-August or T2=2 weeks pre-harvest until T0) and harvest at 95% hull split (mid-August or T0 = nuts at regular grower harvest date). T4 fruits had overall poor quality with higher moisture (from 9% to 20%) than T2 and T0 (6% and 5%, respectively), a higher percentage of insect-damaged fruits (17.5 % for Bakersfield and 13.3% for Chico), a higher count of very molded fruits which was associated with a darker kernel skin reading on the Minolta colorimeter. Fresh kernel weight slightly decreased from T4 (1.4 to 1.1 g) and stabilized at harvest T0 (~1.0 g). For reasons that remain unclear, free fatty acids (FFA) values were significantly higher than the industry standard and the other reported percentage values for the fruits incubated for 2 weeks in Bakersfield than at T4 or T0. Generally, FFA values remained greater than the minimum industry standard of 1.5%. Peroxide Values (P.V.) were below the industry maximum standards (< 5.0 meq/kg) across the treatments. In general, T4 nuts had higher moisture, darker kernel skin, more significant insect damage, and greater mold formation than T2 and T0 while T2 fruits were comparable in quality to regularly harvested fruits (T0). Hence, a slightly early harvest (T2) to optimize off-ground practices does not represent a loss of fruit quality. T4 fruits at harvest were of lower quality; further T4 fruits that remain on the ground for an extended time are of low quality with more significant insect damage and inferior quality than those harvested two weeks from traditional harvest. In traditional harvest T4 and older nuts will be collected, windrowed, and processed with newly shaken nuts; further study is needed to understand how the mixing of T4 with the newly shaken nuts would affect the overall quality of harvested nuts during post-harvest handling phases. Collectively, the results suggest that windfallen nuts that remain on the orchard floor for greater than two weeks have lower quality and are more susceptible to insects and fungal damage.