The California walnut industry faces some challenges, including walnut quality deterioration during the supply chain, cultivar variation, origin fraud, kernel skin darkening, and safety concerns of the byproducts. Walnuts have a high lipid content and most lipids in walnuts contain polyunsaturated fatty acids that are readily oxidized. A higher degree of oxidation is commonly associated with lower quality and increased rancidity. To understand the level of quality degradation during the supply chain, some Californian walnuts sold at retail, in the United States and overseas, were collected and analyzed, and then their quality parameters were compared to those sourced directly from handlers. The data showed that many Californian walnuts sold at retail have undergone oxidation. Many showed higher concentrations of primary oxidation products, indicated by a higher K232 index, than those from handlers. Some also showed higher levels of secondary oxidation products, indicated by a high K268 index and high concentrations of some volatiles. Several samples even showed high concentrations of volatile 2-pentyl-furan, a tertiary oxidation product. Decreased antioxidant capacity is also apparent in many walnuts sold at retail. These findings suggested that a guideline for minimizing oxidation in walnuts during the supply chain was needed for quality improvement.Because Californian walnuts comprise various cultivars, particularly Chandler, Howard, and Tulare, a thorough assessment of their quality was needed to help farmers and handlers select cultivars and to determine if the metabolites could be used for cultivar authenticity. The three cultivars were compared for their quality index, lipids, and phenol metabolites. They were similar in free fatty acidity (FFA), peroxide value (PV), oxidative stability, and the concentrations of total fat, volatiles, delta- and alpha-tocopherols, most of the phenols, most ẟ13Camino acids, all ẟ15Namino acids, all ẟ13Cfatty acids, and all ẟ2Hfatty acids. The data demonstrated that the overall quality of Chandler, Howard, and Tulare was similar. They differed in the concentrations of fatty acids, triacylglycerols, gamma-tocopherol, and chlorogenic acid. Cultivar authenticity was possible when linear discrimination analysis was used on the triacylglycerol data. Like many other agricultural products, walnuts' geographical origin can be subjected to fraud. To help detect the fraud, a database of multiple metabolites and quality indicators of walnuts from various countries was developed. Our data showed that walnuts from varying origins had different 13Camino acids, 2Hamino acids, 13Cfatty acids, and 2Hfatty acids. They also had different fatty acid, phenol, triacylglycerol, and tocopherol profiles. Skin darkening in walnuts is not preferred by the farmers and handlers because walnuts with dark skin receive lower scores during the grading process. Investigating if the skin darkening is associated with quality degradation is necessary. Therefore, we compared the quality index and relevant metabolites of walnuts of light and dark skin. Our observation demonstrated that walnuts with dark skin had significantly lower weight and fat content and higher oxidative stability and volatile concentrations than light walnuts. The dark kernels had larger concentrations of some phenolics like gallic acid, quercetin, and naringenin and lower concentrations of procyanidin B1 and epicatechin gallate than the light walnuts. The walnut industry creates some byproducts, including shells and wood chips. They can be utilized in various products like furniture, fuel, cat litter, and mulch. Because juglone is a quinone in walnut plants that can exert toxicity and allelopathy at high concentrations, it is essential to know its concentration in walnut shells and wood chips. Two methods, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and liquid chromatography connected to a diode array detector (LC-DAD), were compared for their sensitivity, and the LC-DAD method was selected for sample analysis for higher sensitivity. Juglone concentrations in walnut shells and wood chips were lower than what could exert toxicity or allelopathy effects, so they should be considered safe for value-added products.

Avocado oil is a high-value edible oil rich in monounsaturated fatty acids and phytosterols. As consumers seek out healthier and more heat-stable cooking oil, avocado oil has been growing rapidly in popularity. However, the combination of high demand and lack of standards of identity making it difficult to ensure oils are of the quality and purity advertised on the label. Economically motivated adulteration that goes undetected can cause authentic, good quality products to be outcompeted in the market and risks consumer health if an unlabeled allergen is added. The goal of this work was to better understand the chemical composition of avocado oil, or its “fingerprint” so appropriate standards of identity could be created, and so improved adulteration detection methods could be developed. The quality and purity of avocado oils available on the United States market were analyzed to identify the biggest issues in the industry. We found that 82 % of avocado oils were either of poor quality (contained high oxidation and/or hydrolyzation products) or were adulterated. Once the need to develop standards was demonstrated, two different grades of avocados from two regions were collected throughout the harvest season and pressed using a laboratory-scale mill to understand how these variables impacted the quality of the oils. Damaged fruits caused a significant increase in free fatty acidity; however, it was also shown that if good quality fruits were used extra virgin oil could be made from either the whole fruit or the mesocarp. The oils described above plus an additional experimental design that incorporated avocado cultivar assessed how purity parameters vary within authentic avocado oils. Region and harvest time contributed to the largest significant differences in fatty acids and sterols profile. Standards need to be wide enough to accommodate different producing regions, which now includes the United States, Kenya, Peru, and South Africa in addition to New Zealand and Mexico while still minimizing the chance for adulterations to go undetected. New methods using triacylglycerols and cis-vaccenic acid were developed to help support adulteration detection in avocado oil. Cis-vaccenic acid has a higher concentration in avocado oil compared to high-oleic seed oils, which are traditionally difficult to detect in avocado oil, and can be used as a marker of adulteration. By combining triacylglycerol analysis with principal component analysis, adulteration can be detected based on the location of an unknown on the plot, providing an alternative way to detect purity without traditional standards. The findings in this work contribute to ensuring the purity, quality, and safety of avocado oils; help regulators and policy makers to better protect consumers; and support the growth of authentic avocado oil sectors.