Mapping literature review on fermentation substrates for production of lactic acid by Rhizopus SP

Lactic acid has been a great interest to many industries such as food and beverages, cosmetic, chemical and pharmaceutical due to its various functions. It can be produced by Rhizopus sp through fermentation from various substrates such as glucose, starch and lignocellulosic materials. An effective fermentation process depends on the types of substrates which consists of different chemical constituents. This will lead to different production yields. To our knowledge, classification of studies according to the substrates used in the fermentation medium has never been conducted. Thus, the main objective of this study is to classify the earlier works on lactic acid production by Rhizopus sp on the most studied substrates. This study also aims to identify the location or country that focuses on lactic acid production from raw starchy-materials and the production yield. In this study, a mapping literature study was conducted to classify and structure relevant empirical studies into the types of substrates used. Network visualization based on keywords co-occurrences from selected bibliographic databases is included in this study as well. Eleven (11) substrates were identified from 171 empirical studies. Thirty-two (32) studies were discovered to use starch as substrates in lactic acid production by Rhizopus sp. Out of 32 studies, only twelve (12) studies reported the utilization of raw starchy-materials in their studies where most of the studies are reported from the United states. This study redounds to the researchers to uncover critical areas in the production of lactic acid especially in the use of substrates for novel approaches thus, a new hypothesis can be made