Optimization of Pre-treatment Parameters on the Protein Content of the Liquid Extract of Sweet Potato (var. VitAto) for Developing a Plant-based Beverage Intended as a Milk Alternative

Aims: This study aimed to identify the most effective method and optimal parameters for enhancing the protein content during the pre-treatment phase of extracting the liquid component from a local sweet potato (var. VitAto) in developing a plant-based beverage as a milk alternative (PBMA). Study Design: Response surface methodology (RSM) which involved investigating three key factors—percentage of sodium carbonate, ratio of VitAto to alkaline solution, and soaking time—each at three different levels was implemented in this study. Place and Duration of Study: The study was conducted at the Food Science & Technology Research Center, Malaysian Agricultural Research & Development Institute (MARDI), utilizing VitAto sourced from a local farm in Bachok, Kelantan, between August 2021 to July 2022. Methodology: Various treatment approaches were explored, including soaking with water, acidic or alkaline solutions, blanching, boiling, and steaming. Following treatment, the liquid portion was extracted using a heavy-duty juicer and subsequently filtered through cheesecloth. The protein content of the extracts was then quantified using the AOAC method. The pre-treatment method resulting in the highest protein content was chosen for further optimization using RSM. Results: Soaking the sweet potato in an alkaline solution (sodium carbonate), proved to be the most effective pre-treatment method, resulting in a fivefold increase in protein content compared to other methods. The optimal extraction parameters were determined to be a 3.0% concentration of sodium carbonate, a 1:1 ratio of VitAto to alkaline solution, and a soaking time of 20 hours. The predicted protein content under these conditions (2.8 g/100g) exceeded the proposed minimum protein content for PBMA (2.2 g/100g). Conclusion: The optimum parameters for the protein content of pre-treatment in extracting the liquid part of sweet potato (VitAto) for developing PBMA were determined to be 3% sodium carbonate, a 1:1 ratio of VitAto to alkaline solution, and a soaking time of 20 hours.