Nipa Sap Natural Fermentation Strategies to Enhance Its Sugar Content and Bioethanol Derivation

Jasmin binti, Jaraee (2024) Nipa Sap Natural Fermentation Strategies to Enhance Its Sugar Content and Bioethanol Derivation. PhD thesis, University Malaysia Sarawak.

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Abstract

Nipa sap is a sugary sap produced by Nypa fruticans palm. Nipa sap is frequently consumed as a refreshing beverage in several regions across Malaysia. Additionally, it serves as a key ingredient in the production of nipa sugar (gula apong) and vinegar in Sarawak, Malaysia. Nipa sap usually undergo natural fermentation. The natural fermentation of nipa sap poses a challenge in maintaining the quality of the product and apparently, it affects the taste, aroma, and overall content. This makes it less desirable as raw material for gula apong as well as for consumption. Hence, this study aims to enhance the quality of nipa sap by employing multiple strategies to maintain its sugar content. Therefore, it is important to determine the basic properties of the sap that can be a reference to the producer. The sap from nipa palm (Nypa fruticans) was collected from local collectors. Samples were fermented at ambient temperature for 58 days. Physical, chemical, and microbiological analyses were carried out at seven-day intervals, starting from day 0 (fresh tapping) until day 58. Physical and chemical analyses were carried out. The sugar profiles and ethanol content were analysed using High Performance Liquid Chromatography (HPLC), while the volatile organic compound and minerals were analysed using Headspace Gas Chromatography Mass Spectrometer (GC-MS) and inductively coupled plasma - optical emission spectrometry (ICP-OES), respectively. The study reveals that nipa sap is slightly acidic, with a pH of 5.21 ± 0.3, and has a high concentration of total sugars, mainly sucrose (231.5 ± 4.3 g/L), followed by fructose (42.1 ± 1.2 g/L) and glucose (29.7 ± 3.2 g/L). Nipa sap is also found to be a rich source of phenolics and flavonoids and has low glycaemic index (48). The study also identifies four yeast species (Saccharomyses cerevisiae, Candida tropicalis, Cryptococcus humicola, Candida guilliermondii) and three lactic acid bacteria species (Lactobacillus brevis, Lactobacillus casei, Lactobacillus plantarum) present in nipa sap using Analytical Profiling Identification (API) system. In addition, this study shows that hygienic method during collection improved the quality of nipa sap. Total sugar content in the nipa sap collected using the sterilized bottle method on Day 1 (204.66 ± 7.31 g/L) is about 1.5 times higher compared to the bamboo tube method (140.34 ± 5.11 g/L). Apart from that, sterilised bottle significantly slows down the ethanol production during tapping process. Besides, this study also employs different preservation strategies to extend the shelf-life of nipa sap after collection. It reveals that high temperature short time (HTST) preservation method can prolong the shelf life of nipa sap up to 14 days. During this period, sugar level of nipa sap was maintained high whereas only negligible amount of ethanol was produced. Finally, the potential of nipa sap to produce ethanol spontaneously without yeast and nutrient addition was investigated using shake-flask batch fermentation. The study found that nipa sap with commercial baker’s yeast and nutrient supplementation showed the highest fermentation efficiency (Ef) of 91.00%, with a production of 65.5 g/L of bioethanol, which is more efficient compared to nipa sap without commercial baker’s yeast and nutrient supplementation, which had an Ef of 81.21% and produced 57.3 g/L of bioethanol. It should be noted that even without the addition of yeast and nutrients, nipa sap was still able to produce a significant amount of bioethanol, highlighting its potential as a low-cost fermentation substrate. The findings of this study could pave the way for further research in the area and could be used by the industry to develop nipa sap-based products.

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