Abstract
A novel lignocellulose material, holocellulose from rice straw via the pretreatment of SO3 micro-thermal explosion, was developed to produce sophorolipids (SLs) with Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The influence factors of inoculum dose, yeast extract concentration and pH regulators (chemical regents used for adjusting/influencing pH) was investigated and discussed. Results showed that W. domercqiae can grow in the rice straw holocellulose hydrolysate, and acquire relative high SL yield of 53.70 ± 2.61 g/L in shake flask culture. Inoculum dose, yeast extract concentration and pH regulator made obvious influence on fermentation parameters, especially on final broth pH and SLs production. Furthermore, there is a strong negative linear correlation existing between final broth pH and lactonic SL or ratio of lac SL/tot SL. Additionally, comparison between SL production and non-glucose carbon sources, culture methods, microbes in previous reports was carried out. These results will be benefit for acquiring SL mixture with suitable lac SL/tot SL ratio for specific purpose and scope economically.
Highlights
Elemental and scanning electron micro‐ scope (SEM) analysis of rice straw and holocellulose The differences in chemical, elemental and SEM analysis of rice straw before/after pretreatment were compared and the results were shown in Tables 1, 2 and Fig. 1
We could see that rice straw contained 56.02 % of holocellulose and 14.00 % of lignin and lignin content reduced to 5.77 % in holocellulose after pretreatment
The holocellulose content increased to 86.17 %, which is predominantly attributed to the decrease of lignin, water and ash
Summary
Sophorolipids (SLs), an extracellular biosurfactant, are being applied in fields of detergent (Cox et al 2013; Lee et al 2014), petroleum (Sirola 2010), cosmetic (Hillion et al 1998; Morya et al 2013), pharmaceutical (Chen et al 2006; Morya et al 2013; Singh et al 2016), food processing (Cooper and Paddock 1984; Liu et al 2009), environment industries (Sirola 2010), nano material (Pandey et al 2016) and fermentation engineering (Gross et al 2015) for their potential characteristics They have comparable surface activity, biodegradability, biocompatibility, and low toxicity compared with chemical surfactants (Banat et al 2000; Lee et al 2008). Both choosing new substrates to lower production cost of SLs and selectively synthesis of SLs by optimizing fermentation conditions are hot topics.
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