Optimization of Pistachio Kernel Cellulose Extraction using Response Surface Methodology: Effects of Key Processing Factors

Introduction

Asian pistachio (Pistacia vera L.) is a popular nut crop known for its unique flavor, high nutritional value, and health benefits,¹ which constitutes about 50% of the weight of the nut.² It is native to West Asia, especially in northeastern Iran and northern Afghanistan, where the pistachio tree formed an important part of the local semi-arid aromatic forest.^3,4 According to a survey, the United States produces 47 % of the pistachio, followed by Iran (38%) and turkey (9%) in the world market.⁵ Asian pistachio kernel also contains several bioactive compounds,⁶ such as polyphenols, tocopherols and phytosterols popularly known for their beneficial health effects.² Polyphenols are known for their antioxidant and anti-inflammatory properties, while tocopherols are important antioxidants that can protect against oxidative stress.⁷ The phenolic compounds and the oxidizing activity of pistachio decrease with an increase in the ripening period. The core of Asian pistachio (Pistacia vera L.) is made up of protein of 15.0 - 21.2%^8,9 fats of 55.2 - 60.5%,¹⁰ carbohydrates

14.9 - 17.7%¹¹ moisture of 2.5 - 1%,¹² ash of 2.2 - 2.5%,¹² 13 phenolic compounds¹³ and fiber.^14,15The fiber content varies from 4.8% to 10.6% and makes it a potential source of cellulose.¹⁶ Cellulose, being the most abundant raw material on earth, is produced commercially through several plants every year because of its substantial involvement in a variety of potential applications. It can be used in the paper, textile, and food industries along with its utilization in pharmaceutical and biomedical applications.¹⁷ because of its several health benefits, which include reducing the risk of chronic diseases such as diabetes, cardiovascular disease, and colon cancer.¹⁸ Cellulose is referred to as a non-toxic major constituent of plant material that can be extracted from higher plants like wood, cotton, flax, hemp, jute, sugarcane bagasse, ramie, cereal straws, etc.¹⁹ It is said to be renewable and acts as a polysaccharide filler.²⁰ It is the most abundant biopolymer in the world, with an estimated 1010-1012 tons produced annually, and primarily consists of lingo-cellulose which includes cellulose, lignin, and hemicellulose.²¹ Lignin is a highly cross-linked phenolic polymer, while hemicellulose is a branched...