**6. Utilization of tree nut processing wastes for value-added byproducts**

Besides kernels, a large amount of waste materials, mainly the shells and hulls, is generated during tree nut processing and production. In fact, the tree nut hulls and shells account for 70% of the harvested weight [140], but currently have low economic values. Utilization of these wastes for producing value-added byproducts or bioenergy should benefit the stakeholders economically and reduce the environmental impacts of tree nut processing industry.

Hulls usually have high contents of natural antioxidants, such as tannins and phenolics [141]. Extraction of these antioxidants and then adding them as functional additives to other foods may improve the economic value of the crop [142]. Extracts from walnut and pistachio hulls exhibit good antibacterial and antiinflammatory properties [143]. Walnut hull also contains juglone, a compound with high pharmaceutical value, which can be extracted and used in medicines [144]. Almond hulls weights over 60% at harvest and are conventionally used as cattle feed in California and Australia [145]. However, they are normally sold at a very low price. In addition, hulling and shelling of almonds cost about \$0.30/kg, being one of the most expensive operations in the almond industry. Therefore, these processes need to be optimized to reduce the processing cost. Besides, off-ground harvested almonds have much higher MCs in the hulls at the time of harvest [54]. Wet dehulling of the almonds will be needed, as drying the hulls consumes more


#### **Table 1.**

*Valuable substances and potential applications of wastes and byproducts from tree nut processing.*

#### *Processing of Tree Nuts DOI: http://dx.doi.org/10.5772/intechopen.102623*

than half of the total drying energy and leads to extra drying time and costs [24]. Meanwhile, since the high moisture hulls have high sugar contents, they can be used for fermentation and bioenergy production, and culturing certain microorganisms for producing value-added foods or biodegradable plastics without the need of drying [146–150]. Tree nut shells are mainly composed of cellulose, hemicellulose, and lignin [151], and thus can be used as woody biomass for biogas production through combustion or pyrolysis [152, 153]. The natural biopolymers from the tree nut production wastes and byproducts, such as polysaccharides, fibers, and proteins could also be utilized and manufactured into thin films as biodegradable packaging for foods [154]. The natural bioactive compounds in the hulls can be added into the packaging to improve the antioxidative and antimicrobial functions [155]. **Table 1** provides a summary of the potential values and applications of tree nut production wastes and byproducts.
