Project : USDA ARS

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Research Project: Zero Waste Agricultural Processing

Location: Bioproducts Research

2021 Annual Report

Objectives
Food processing losses can represent up to 40 percent of the initial harvest, resulting in significant environmental and economic costs. With stakeholders like the Almond Board of California committed to achieving zero waste, we aim to create viable bioproducts from agricultural byproducts, everything from field to table. The first objective is to add value to a low-value almond processing coproduct, the hulls, which are the bitter, but sugar-rich fruit of the almond tree, by: (1) creating a phenolic-rich sweetener for human consumption; (2) extracting sugar from almond hulls for use in bee diets during the winter, and (3) developing cost-effective carbon feedstock for fermentation that produces bioplastics and specialty chemicals. With a commercial partner we will optimize a novel fermentation process to convert food waste (including hulls) into a commercially-viable family of bioplastics specifically polyhydroxyalkanoates (PHA) using the latest techniques in biotechnology. Objective 1: Develop sustainable technologies toward “zero waste” production by converting food waste, byproducts and under-utilized biomass streams into marketable plastics, specialty chemicals, additives, and active agents. • Sub-objective 1A. Add value to almond hulls. • Sub-objective 1B. Convert food waste and under-valued byproduct streams into bioplastics]. • Sub-objective 1C. Convert pectin-rich citrus peel waste, sugar beet biomass, and almond hulls into aldaric acid and aldonate bioproducts. Objective 2 focuses on optimizing new uses for underutilized agricultural fibers. In collaboration with several commercial partners, we plan to scale up torrefaction (heating biomass to 200-300 'C), to convert tree nut shells and hemp residue into functional fillers that will improve commodity plastics. We also propose to convert underutilized polysaccharides like pectin, alginate, and xylan were isolated from enzyme conversion processes into industrially-relevant environmentally friendly diacids such as aldaric acid for use as solvents in homecare products. Our group has developed a wide array of enzymes to deconstruct plant cell walls. These enzymes will be used, via combinatorial enzymatic strategies and in vitro reaction schemes, to create “designer oligosaccharides” and green chemicals that meet specific marketable needs. Objective 2: Optimize end-use technology for underutilized agricultural fibers, including straw residue, bagasse, and grasses by developing commercially-viable chemicals and nanoparticles for novel applications including nanocomposites. • Sub-objective 2A. Apply thermochemical conversion technology to add value to tree nut shells and underutilized crop residues including hemp. • Sub-objective 2B. Convert biomass into designer oligosaccharides using combinatorial enzyme technology.

Approach
Objective 1: Develop sustainable technologies toward “zero waste” production by converting food waste, byproducts and under-utilized biomass streams into marketable plastics, specialty chemicals, additives, and active agents. Sub-objective 1A. Add value to almond hulls. Sub-objective 1B. Convert food waste and under-valued byproduct streams into bioplastics. Sub-objective 1C. Convert pectin-rich citrus peel waste, sugar beet biomass, and almond hulls into aldaric acid and aldonate bioproducts. Objective 2: Optimize end-use technology for underutilized agricultural fibers, including straw residue, bagasse, and grasses by developing commercially-viable chemicals and nanoparticles for novel applications including nanocomposites. Sub-objective 2A. Apply thermochemical conversion technology to add value to tree nut shells and underutilized crop residues including hemp. Sub-objective 2B. Convert biomass into designer oligosaccharides using combinatorial enzyme technology.

Progress Report
In support of Sub-objective 1A, research with a major mushroom producer continued on using almond hulls as a ground cover, called casing, for mushroom production. Presently the mushroom industry uses sphagnum peat, a natural sediment formed in “peat bogs” over thousands of years under anaerobic conditions. Sphagnum has proven to be an “ideal” mushroom casing, but it is not really a renewable resource, and it is a limited resource produced in limited locations. ARS researchers continued to investigate the use of so-called “spent hulls”, almond hulls after their sugar have been extracted, as a replacement for sphagnum peat for mushroom production. It was shown that spent hulls absorb/adsorb up to 5 times their weight in water, which is comparable to sphagnum peat. Preliminary results show that mushroom production using spent hulls was on par or greater than rates seen with sphagnum peat casing. The use of spent almond hulls could addresses multiple agricultural needs by (1) providing a cost-effective, sustainable replacement material for imported sphagnum peat., (2) creating new markets for almond hulls, and (3) developing a cradle-to-cradle solution for an array of almond byproducts. For Sub-objective 1B, ARS researchers in Albany, California, in collaboration with a commercial producer of bioplastics, discovered a synthetic pathway to create a polyhydroxyalkanoate copolymer with increased elasticity. The standard and most readily produced bioplastic derived via bacterial production is often the brittle, highly crystalline poly(3-hydroxybutyrate) form. Using an understanding of the metabolic pathway toward biosynthesis, USDA researchers adjusted the final product to create a co-polymer of poly(3-hydroxybutyrate) with poly(4-hydroxybutyrate). This copolymer is more ductile than the simple homopolymer. While the U.S. nut industry is growing, markets for nut byproducts, particularly nutshells and tree pruning’s, have not kept pace. Progress on Sub-objective 2A included continued research into torrefaction as a thermochemical process to improve physicochemical properties of almond, walnut, and pistachio shells. Torrefaction consists of thermal treatment of biomass at temperatures between 200 and 300 °C in the absence of oxygen, where final material properties of the torrefied biomass depend on the temperature, heating rate, and residence time. In general, torrefied biomass exhibits higher hydrophobicity and calorific value with reduced moisture absorption compared to untreated biomass, making it an ideal fuel source for energy applications compared to raw biomass. Recently, almond shells of soft, semi-soft, and hard-shell varieties, as well as walnut shells and almond wood, were torrefied at two different temperatures (230 and 290 °C) and three different residence times (20, 40, and 60 minutes) in order to characterize the physicochemical properties. The thermal behavior of raw and heat-treated biomass was investigated by thermogravimetric analysis (TGA) analysis, elemental analysis, pH, helium pycnometry, Fourier transform infrared (FTIR) spectroscopy, and dynamic vapor sorption analysis to optimize their end-use mechanical properties. These included (1) application in rubber tire formulations as carbon black substitutes, (2) use in recycled plastics to make, for example, industrial composites, and (3) development of activated carbons for air and water filters. The last research topic has become a topic for commercial development via a CRADA agreement to develop activated carbon matrices that store hydrogen or methane for fuel cell development. In support of Sub-objective 2B, oligosaccharides with tailored properties, termed “designer oligosaccharides,” were successfully produced by applying combinatorial enzyme technology to under-utilized plant fibers. Libraries of different compounds were developed and then tested for specific properties. A paper was submitted and is under review in Current Biotechnology that is the first publication to review the theory, mechanism, and methodology of combinatorial enzyme technology. This technology was invented and developed by ARS researchers in Albany, California, to create specific functional molecules for use in nutraceuticals, antibiotics, prebiotics, and gelling agents. Work continues to test newly derived non-digestible oligosaccharides (NDOs) as food ingredients as these active agents gain acceptance as active nutraceuticals or prebiotics, mostly oligosaccharides derived from fructose or galactose.

Accomplishments
1. Proteins are utilized to extract bitter-tasting tannins from almond hull sugars. Almond hulls, the fruits of almond trees, are rich in extractable free sugars which could be used in feed or even food applications if sugars could be extracted effectively and safely; however, hulls carry phenolic compounds that render them too bitter for most foods. ARS researchers in Albany, California, tested a series of food-grade proteins as a means to remove bitter-tasting phenolic compounds (tannins) from hull sugar syrups. Fish gelatin proved to be the most effective protein for removing tannins from syrups, compared to other proteins traditionally applied, such as sodium, casein, whey or zein. The addition of 1% fish gelatin removed up to 85% of bitter tannins, resulting in a unique natural sugar solution that can now be further tested in tasting panels for human consumption. Creating food-grade sweeteners from almond hulls could add hundreds of millions of dollars to the value of hulls, a direct benefit to the industry.

U.S. DEPARTMENT OF AGRICULTURE

Bioproducts Research: Albany, CA