IMAGINATION INNOVATION

Capturing Maximum Genetic Potential at kernel moisture, color, texture, lipids, tocopherols (vitamin E), cyanogenic glycosides and free amino acids.

The research study presented at the 2022 Almond Conference involved new experimental almond varieties and commercial varieties. One finding was that on average, the experimental varieties have higher levels of total vitamin E. This translates into longer shelf life, and greater nutritional value. Cyanogenic glycosides are responsible for almond bitterness and almond aroma.

Amygdalin is a cyanogenic-glycoside. Monitoring amygdalin in almond kernels and characterizing levels in almond hulls is critical for maintaining a safe, high-quality product and identifying safety of co-products.

Quality management at the processor involves early detection of insect pests in product storage. UC Davis researcher Zhongli Pan said at the Almond Conference that current chemical fumigation and product loss costs $350 million annually for tree nuts alone in the U.S. (see related article on page 30.)

Since 2021, he has been testing a new technology aimed at detecting insect infestations in stored almonds. Insect infestations can cause significant damage to stored almonds in a short time, Pan said. Infestations can occur quickly before they can be detected by humans. The SmartProbe technology, he said, is a novel tool for early detection of insect pests in stored commodities. Studies over the past two years showed it can detect insect infestations at an earlier stage than human inspection. One insect, he said, can damage 25% of kernels in a bin stored at 30 degrees Celsius. Insects found include navel orangeworm larvae and moths, red flour beetles, bugs and moths. The device measures temperature and relative humidity and monitors storage conditions.

Postharvest stockpile management of almonds and use of gaseous chlorine dioxide fumigation was explained by USDA-ARS researcher Vivian Wu. This fumigant reduced A. flavus mold and toxins on stockpiled almonds with no significant effect on almond quality. She said gaseous CO2 can be used for moisture pockets and moisture exposed product. It does not require on-site storage of gas cylinders and no certification for application is required. This chemical can be modified on the company’s required treatment method for storage, stockpile or silos.

Walnut Challenges

In walnuts, sunburn, irrigation management and disease prevention can determine kernel quality at harvest.

Dark kernels, shriveled kernels and mold are quality defects that cause processor rejections.

Producing light-color kernels is important in the walnut industry. Robert Verloop, executive director of California Walnut Board and California Walnut Commission, said at the UC Tri-County Walnut Day. Light-color kernels give handlers more flexibility in marketing as they can be held for a longer period.

Environmental conditions in walnut orchards cannot always be mitigated as evidenced by the summer 2022 heat wave that caused serious nut damage in many northern growing regions. Very high temperatures at critical times in nut development caused hulls to adhere to shells. These ‘black hull’ nuts were rejected at the hullers.

UC Plant Pathologist Bruce Lampin- en, in a presentation at the Tri-County Walnut Day, highlighted the walnut quality studies that have taken place over many years. They included quality and kaolin application studies and impacts of excessive irrigation on quality. One of the findings was nuts that have hulls that do not split normally and maintain wet conditions around the kernel cause quality problems.

Nuts continuously exposed to the sun have husks that develop dark brown leathery lesions by mid- or late summer. Sunburned nuts have shriveled and darkened kernels. Lampinen said field trials showed most sunburn occurred in southwest-oriented lower positions where there was an indentation in the canopy, likely leading to lack of air circulation. Kaolin, which is applied to prevent sunburn, needs to be applied where nuts are exposed to mid-day sun.

Lampinen noted timing of stress has different impacts on quality. Stress during kernel filling, typically in July and August, impacts kernel size. Stress at hull split can impact kernel color.

Water availability and uncertainty and warmer summer temperatures will continue to challenge walnut quality statewide, Lampinen said.

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