ABSTRACT
A wide variety of nutraceutical compounds, food additives, and foodstuffs may be produced through the bioconversion of substrates contained in agricultural crops and residues. Bioconverted products include traditional foods and beverages such as beer, wine, vinegar, yogurt, tofu, and baker’s yeast. Bioconverted nutraceutical and food products used in the food industry range from
flavor compounds
(roasted, nutty flavor of pyrazine produced through aerobic solid-state fermentation of soybeans by bacterium
Bacillus subtilis,
fruity flavor of citronellol, linalool, and geraniol produced by yeast
Kluveryomyces lactis
,
vanillin flavoring produced by
Pseudomonas
and
Corynebacterium
,
and bioflavors for beer produced by
Saccharomyces cerevisiae
);
essential fatty acids
(omega-3 and omega-6 fatty acids eicosapentaenoic (EPA) and arachidonic (ARA) acids from aerobic submerged fungal cultures of
Pythium irregulare
,
Mortierella elongata
, and
Mortierella alpina
using soybean and rice bran substrates,
and omega-3 fatty acid docosahexaenoic acid (DHA) and EPA from algal sources such as
Gonyaulax, Gyrodinium,
and
Cryptoconidium
);
organic acids
(citric acid produced by aerobic fermentation of sugarcane or beet molasses by
Aspergillus niger
or
Candida lipolytica
,
lactic acid produced by
Lactobacillus helveticus
from concentrated cheese whey,
and pyruvic acid production by variety of yeasts and bacteria
);
pigments
(the carotenoid pigment and antioxidant astaxanthin produced by
Xanthophyllomyces dendrorhous
,
red pigments produced by fungi
Paecilomyces sinclairii
during aerobic fermentation of sucrose and starch,
and orange and red dyes produced by submerged culture of
Monascus purpureus
from hard wheat substrate
);
emulsifiers
(biosurfactants produced by filamentous fungi
Curvularia lunata
,
and high molecular weight emulsifiers produced by yeast
Candida utilis
);
vitamins
(vitamin B
production by prokaryotic bacteria
Propionibacterium shermanii
and
Pseudomonas denitrificans
,
or mixed cultures of methanogens,
and vitamin K
-7 production by bacterium
Bacillus subtilis
using fermented soybeans
); and
sugar substitutes
(xylitol produced from microaerobic fermentation of D-xylose contained in hydrolysates of sugarcane bagasse, rice straw, and other lignocellulosic material and defined media by yeasts such as
Candida
and
Pichia
). Bioprocess design involves consideration of all critical unit operations, including
feedstock pretreatment and hydrolysis, bioreactor modeling and design, and extraction and separations technologies. Bioreactor modeling and design based on microbial growth and product formation kinetics may be used to optimize production of high-value compounds by a range of natural microorganisms such as fungi, bacteria, yeasts, and algae and recombinant organisms. Steps to the design based on microbial kinetics include expression of growth, decay, and product formation rates; development of mass-balance models of the bioreactor; simulation of substrate, biomass, and product concentrations and rates of biomass and product formation for various reactor configurations; selection of reactor configuration; and design optimization to maximize product formation rate or product concentration based on simulation. The focus of this chapter is on microbial modeling and bioreactor design for suspended growth, shear-tolerant, natural cells. Many bioprocessing examples could
serve to illustrate the kinetic approach to modeling and design; we will highlight the bioconversion of xylose to the sugar substitute xylitol.
