Future Cereal Starch Bioengineering: Cereal Ancestors Encounter Gene Technology and Designer Enzymes

Abstract

The importance of cereal starch production worldwide cannot be overrated. However, the qualities and resulting values of existing raw and processed starch do not fully meet future demands for environmentally friendly production of renewable, advanced biomaterials, functional foods, and biomedical additives. New approaches for starch bioengineering are needed. In this review, we discuss cereal starch from a combined universal bioresource point of view. The combination of new biotechniques and clean technology methods can be implemented to replace, for example, chemical modification. The recently released cereal genomes and the exploding advancement in whole genome sequencing now pave the road for identifying new genes to be exploited to generate a multitude of completely new starch functionalities directly in the cereal grain, converting cereal crops to production plants. Newly released genome data from cereal ancestors can potentially allow for the reintroduction of cereal traits including, for example, health‐promoting carbohydrates that may have been lost during domestication. Raw materials produced in this manner can be processed by clean enzyme‐assisted techniques or thermal treatment in combination to further functionalize or stabilize the starch polymers. Importantly, such products can be multifunctional in the sense of combined food/material or food/pharma purposes, for example, edible plastics, shape memory materials, and cycloamylose carriers and stabilizers for diverse bioactives.

Starch meets biotechnology : in planta modification of starch composition and functionalities

“…GWD2 and GWD3 were found in a wide range of organisms, while GWD2 was identified in very few higher plants, corroborating previous reports (Baunsgaard et al, 2005;Glaring et al, 2007). Unlike previously described (Glaring et al, 2007), GWD2 is not exclusive to dicots but also present in monocots, such as Brachypodium distachyon and Hordeum vulgare (Blennow et al, 2013;Radchuk et al, 2009;Tanackovic et al, 2014b). This result confirmed the assumption that the duplication of GWD occurred before divergence of monocots and dicots.…”

Structure of branching enzyme- and amylomaltase modified starch produced from well-defined amylose to amylopectin substrates

“…Enzymatic modification of starch is gaining an interest as a clean and safe alternative to chemical modification (Blennow et al, 2013). Such enzymatic starch modification may be carried out either by the use of recombinant enzymes acting on purified starches, or alternatively the enzymes may be expressed directly in the starch producing crops by GM technology (Hebelstrup et al, 2015).…”

“…In vitro, BE also catalyses a cyclisation reaction to form cyclo-amylose and cylo-amylopectin cluster (Kelly, Dijkhuizen and Leemhuis, 2009;. Starch modification with BE demonstrates an increase in solubility, reduced viscosity and for AM, increase degradative resistance of the product (Blennow et al, 2013). The thermostable BE from R. obamensis has drawn interest in starch modification to efficiently produce highly-branched α-glucans (Roussel et al, 2013;Shinohara et al, 2001).…”

Recent progress toward understanding the role of starch biosynthetic enzymes in the cereal endosperm

“…The degradation of sucrose derived from photosynthesis has also been included because of its significant contribution to the synthesis of ADP-glucose and seed sink strength. For the potential application of these enzymes for future cereal starch bioengineering and some other complementary information of, e.g., granule initiation and control of starch granule size, please refer to recent reviews like [4][5][6]. Throughout this review, affiliation of individual starch metabolizing enzymes to various families of glycoside hydrolases (GH) and glycosyl transferases (GT) as well as their carbohydrate-binding modules (CBM) reflects their classification within the CAZy database (http://www.cazy.org/).…”