UC Davis

Almonds are an important crop for California and are an intrinsically nutrient-dense food, containing approximately 20% protein and 50-55% fat. Despite this, almond milk, a popular non-dairy beverage, is typically quite low in nutrients, containing only ~0.5% protein and ~1.25% fat. Most commercial almond milk is made by suspending a finely ground roasted almond paste in water with hydrocolloids and emulsifiers, which help keep the solids in suspension and improve mouthfeel. Due to this production method, the quantity of almond paste that manufacturers can use without solids settling out of solution is limited. Therefore, there is significant potential for both nutritional and sensory improvements through the development of alternative processing methods for almond milk.The overarching goal of this thesis was to develop and optimize environmentally friendly sustainable processes such as aqueous (AEP) and enzyme-assisted extraction processes (EAEP) to produce almond milk with enhanced nutritional and sensory properties. AEP and EAEP enable the simultaneous extraction of proteins and lipids from organic matrices through protein solubilization and washing out of lipids into the aqueous medium. Extractions are performed under constant agitation and controlled pH and temperature conditions. The extraction is followed by centrifugation to separate the protein- and lipid-rich supernatant from the fiber-rich “insoluble” fraction. In the EAEP, enzymes like proteases can be added during the extraction to improve the solubilization of the proteins. Additionally, the use of enzymes can significantly impact the properties of the extracted proteins including their functionality, flavor, and biological activity. This thesis proposes the use of AEP and EAEP to produce almond milk that is rich in proteins and fats, is well-accepted by consumers, and is feasible for production. Chapter 1 details the state of the art in retail non-dairy milks, using almond milk as a case study. Recent studies on emerging processing technologies for almond milk are presented, including a detailed explanation of AEP and EAEP processes, their mechanisms, and their potential as processing methods for almond milk. Chapter 2 explores how preprocessing parameters (degree of roast and degree of grind) and methods (AEP vs. EAEP) affect the overall process extractability and the nutritional composition of the milks. Some particle size reduction is necessary for AEP and EAEP to free trapped materials from within cellular structures; therefore, the impact of degree of grinding was investigated. Almonds are typically roasted before grinding into paste, as roasting facilitates grinding through oil release and cell wall shrinkage and imparts desirable flavors to almonds. However, roasting can also denature proteins, potentially affecting their extractability. Consequently, the impact of degree of roast was also investigated. Three degrees of roast (unroasted, light roast, dark roast) and three degrees of grind (flour, butter, paste) of almonds were applied to almonds, resulting in a total of nine raw materials, each subjected to AEP and EAEP. The effects of roasting and grinding levels on protein and lipid extractability, as well as protein properties such as proximate composition, digestibility, surface charge, secondary structure, and surface hydrophobicity, were evaluated. Finer particle size was associated with higher extraction yields while increased roasting was found to reduce protein extraction, likely due to protein denaturation and aggregation. Based on yields, milk composition, and energy requirements, light-roasted almond butter was selected as the optimum material for almond milk production.

Chapter 3 builds off this knowledge, utilizing a commercially purchased food-grade light roasted almond paste to further investigate the impact of extraction parameters on the physicochemical and sensory properties of the milk. An innovative experimental design was employed in this study, utilizing both sensory and physicochemical feedback to optimize process development. Central composite designs (CCDs) were used for both AEP (varying levels of pH and solids-to-liquids ratio) and EAEP (varying levels of protease and solids-to-liquids ratio) for measuring the impact of these variables on physicochemical parameters such as extraction yields, protein content, protein immunoreactivity and antioxidant activity, and sensory descriptors of the milks such as creaminess, mouthfeel, bitterness, and nutty flavor. After initial descriptive analyses, six formulas were selected for further hedonic analyses, which led to a subsequent refinement of extraction parameters and a final hedonic analysis. Almond milk formulas with increased lipid and protein content and positive consumer acceptance were produced using both AEP and EAEP methods. In Chapter 4, the selected AEP and EAEP formulations (Chapter 3) were scaled up to identify potential pitfalls. Previously performed at bench scale, extractions were performed in larger (15 L) quantities and subjected to ultra-high temperature (UHT) sterilization and homogenized at pilot-scale. These were compared with a typical “commercial” formula using the suspended solids method. These milks were then evaluated for proximate composition and protein properties (immunoreactivity, antioxidant activity, digestibility), as well as for emulsion stability, lipid oxidation, and viscosity over their shelf-life. AEP and EAEP milks were both significantly higher in protein and fat than the commercial milk formula, with enzyme leading to milks with reduced immunoreactivity and increased antioxidant activity. AEP and EAEP milk proteins exhibited significantly higher in vitro protein digestibility than the commercial formula. Oil oxidation was low over the shelf-life of all milks. This work demonstrates the feasibility of scaling up these methods for large-scale production of these products. In this work, we present a method for manufacturing almond milk with improved nutritional qualities and tailored physicochemical properties. The optimization of upstream processing and extraction parameters, driven by sensory and analytical data, was crucial for selecting conditions for scaling-up of these methods. This work offers almond milk processors the opportunity to develop nutritious products that appeal to consumers.