Abstract
Candida maltosa was cultivated in the liquid phase of residual brewing yeast, a major brewery residue, to produce biomass and biofilm. Using response surface methodology, the effect of two variables at two different levels was investigated. The independent variables were agitation speed (at 100 and 200 rpm), and aeration (at 1 and 3 L min−1). Aeration was identified to be important for the production of both biomass and biofilm, while agitation was the only factor significantly affecting biofilm production. The maximal production of biofilm (2.33 g L−1) was achieved for agitation of 200 rpm and aeration of 1 L min−1, while the maximum for biomass (16.97 g L−1) was reached for 100 rpm agitation and 3 L min−1 air flow. A logistic model applied to predict the growth of C. maltosa in the exponential phase and the biofilm production, showed a high degree of agreement between the prediction and the actual biomass measured experimentally. The produced biofilms were further characterized using Fourier-transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). FTIR allowed the identification of methyl, carbonyl ester and sulfate groups, and revealed the presence of uronic acid moieties and glycosidic bonds. Water-retention ability up to relatively high temperatures was revealed by TGA, and that makes the produced biofilm suitable for production of hydrogels. SEM also gave indications on the hydrogel-forming potential of the biofilm.
Highlights
The scarcity of high-quality food is one of the most acute problems of human civilization and exploring new food sources is an urgent requirement for fulfilling the “zero hunger” Sustainable Development Goal [1]
The good cultivation performance revealed that no nutrient supplementation of the medium was required for C. maltosa growth, since the conditioned Residual Brewing Yeast (RBY) supernatant was already rich in nutrients resulting from the lysis of brewer’s yeast
(3.8 g L−1 ) was high enough to make it unnecessary to supplement the medium with external nitrogen sources.The biomass production ranged between 13.17 g L−1, for the experimental run with 1 L min−1 of air flow and 200 rpm agitation, and 16.97 g L−1 for
Summary
The scarcity of high-quality food is one of the most acute problems of human civilization and exploring new food sources is an urgent requirement for fulfilling the “zero hunger” Sustainable Development Goal [1]. Protein is an important component of the human diet but reaching the requirements of the increasing world population can cause disproportionate growth of meat and dairy production or uncontrolled increase in land usage for producing leguminous seeds. Inclusion of SCP in the human diet can contribute to satisfying our protein requirements without unsustainable expanding livestock production for animal protein or arable land for plant-based protein. SCP has interesting advantages over other protein sources, and it can be obtained through microbial cultivations, with high productivities, and independence of seasonal factors from a wide variety of raw materials [3]. During the 1970s, production of so-called protein-vitamin concentrate using different yeast species of the Candida genus grown on biomass-based substrates and even on n-alkanes became a widely distributed industrial process in the Soviet Union and other East European countries [2]
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