## 4 Discussion
All of the pH of FMB with starter culture was in the range of TCPS regulation from the beginning of fermentation onward. However, the pH of FMB without starter culture was less than pH 4.3 after fermentation 200 h. Total acidity as a percentage of lactic acid equivalent was increased in FMB with a starter. _L. plantarum_ SK15 was one of LAB that could produce lactic acid from the anaerobic microbial breakdown of carbon source (sugar cane) during the process [39]. The level of methanol in a beverage is one of the strictest regulations for the food industry and consumer safety. The permissible level of methanol in fermented plant beverages is 240 mg/L according to TCPS. Another confirmation was used as an indicator of the safe methanol level. The presence of methanol should be less than 8% in spirit beverages [28]. In this study, the methanol level was not found in FMB samples. It might be that the mushroom contained a low level of pectin, which is located at the cell wall during ripening. Pectin can produce methanol by removing methyl groups with pectin methylesterase [26]. The permissible level of ethanol in beverages was less than 3% (\(v/v\)) with reference to TCPS. All of FMB were within the acceptance limit of ethanol. In the natural fermentation process (without _L. plantarum_ SK15 as a starter culture), the ethanol content of FMB was higher than FMB with _L. plantarum_ SK15. This proves that the use of starter culture _L. plantarum_ SK15 could reduce the ethanol content in FMB. The possible reason for the elevated level of ethanol might be the contamination of some microorganisms that might contaminate from soil or water in raw mushroom material during fermentation and production. For example, yeast, which is contaminated with H. erinaceus, could change the sugar to alcohol by aerobic reaction [33]. Excess intake of ethanol leads to high blood alcohol concentration, increases osmolality, and the accumulation of metabolites can cause high anion gap metabolic acidosis, acute renal failure, or unexplained neurologic disease [40]. In general, amounts of amino acid precursors were related to their corresponding biogenic amines. The total amino acid decreased from 998.05 to 845.80 \(\upmu\)g/L in a sample with _L. plantarum_ SK15 starter culture. Because amino acid was the precursor of biogenic amine, which could be metabolized during the fermentation process, the fermented beverage added starter had higher proteolytic activity. It enhanced catabolite in free amino acids to other products [37]. The decreased amino acid (precursors of biogenic amine) affects the reduction of biogenic amine accumulation. The present report is related to the previous study of _L. sakei_ BCC102 and Debaryomyces hansenii BCC 106 as a starter culture in Nham fermentation process for five days. The content of total free amino acid content in Nham inoculated _L. sakei_ BCC102 and mixed _L. sakei_ BCC102, and _D. hansenii_ BCC 106 culture decreased by 13.3% (from 31.83 to 27.43 mg/100 g sample) and 19.73% (from 30.97 to 24.86 mg/100 g sample) [37]. From previous literature, arginine is a precursor of PUT and SPD. The arginine in the sample with _L. plantarum_ SK15 starter culture was 23.30 and 23.40 \(\upmu\)g/L at 0 and 720 h, respectively. The nonsignificant change of the arginine content might be due to other PUT and SPD formation pathways from ornithine [14]. The changes in amino contents may be due to these amino acids being used for the growth of the microorganisms and might be metabolized to flavors [41]. The report confirmed that amino acids can reform to other compounds. Aspartic acid could be converted to sweeteners (asparatame). Leucine, threonine, and valine can change to volatile compounds. Serine transforms to glycine. Glutamic acid is well-known to exhibit umamitype flavor and is widely used in the food industry. Aspartic acid also imparted umami taste in foods. The starter culture addition affects a reducing sugar content. The natural fermentation process involved lower reducing sugar content than FMB with _L. plantarum_ SK15.