Bioplastics from potatoes


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Scientists at Texas A&M University are learning how to alter the ratio of potatoes' two starch molecules.

ALTERING the ratio of two starch molecules in potatoes, amylose and amylopectin, will help increase both culinary and industrial applications, according to US scientists.

Amylose consists of linear, helical chains of 500 to 200,000 glucose monomers, whereas amylopectin molecules are huge, branched polymers of glucose, each containing between one and million residues. Both amylose and amylopectin consist of alpha D glucose units. 

Waxy potatoes are high in amylopectin content, and have applications in the production of bioplastics, food additives, adhesives and alcohol. 

Two articles, outlining how CRISPR (Clustered regularly interspaced short palindromic repeats) technology can advance the uses of the world's largest vegetable crop, were recently published in the International Journal of Molecular Sciences and the Plant Cell, Tissue and Organ Culture journal. 

In a statement released by Texas A&M University, Keerti Rathore, one of the researchers involved in the studies, said the information and knowledge they gained from these two studies will help them introduce other desirable traits in these very important crops.

The main factor which determines a potato's use is the amount of starch. Isabel Vales, who co-authored both the papers, said 
Potato starch can also be used to produce ethanol for fuel or in beverages like vodka; as a biological substitute for plastics; or as adhesives, binders, texture agents and fillers for the pharmaceutical, textile, wood and paper industries, and other sectors, according to the researchers.

The amount and type of starch in a potato are important considerations for industrial applications. According to Stephany Toinga, one of the authors on both the papers, starches higher in amylopectin are desirable for processed food and other industrial applications due to their unique functional properties.

For instance, starches higher in amylopectin are the preferred form for use as a stabiliser and thickener in food products and as an emulsifier in salad dressings. Since amylopectin starch has freeze-thaw stability, it is used in frozen foods. Also, potatoes rich in amylopectin starch yield higher ethanol levels compared to those with other starches.

What Are The Benefits Of Breeding Potatoes With Select Starches?
Toinga said that developing potato cultivars with modified starch could open new opportunities. In the study published in the International Journal of Molecular Sciences, Toinga described the gene-edited Yukon Gold potato strain. This potato was developed in the 1960s by Garnet Johnston in Canada. Similar to Yukon Gold, potatoes with high amylopectin and low amylose have industrial applications beyond traditional uses. 

Benefits Of Potatoes With High Amylose And Low Amylopectin
Vales said that potatoes with high amylose and low amylopectin would be desirable for human consumption because the amylose acts like fibre and does not liberate glucose as easily as amylopectin. This results in a lower glycemic index, and makes potatoes more acceptable for people with diabetes. The glycemic index is a system of assigning a number to carbohydrate-containing foods according to how much each food increases blood sugar. The number is assigned based on how quickly and how high those foods cause increases in blood glucose levels. 

Low glycemic index foods are the ones with a glycemic index value of 55 or less, and include most fruits and vegetables, grains, beans, pasta, low-fat dairy products and nuts. 

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How Did CRISPR-Cas9 Create New Options?
According to Vales, CRISPR-Cas9 technology has expanded the toolset available to breeders, and represents a more direct, faster means to incorporate desired traits into popular commercial crop varieties. Though the same can be achieved through conventional breeding, it is a lengthy process that can take 10 to 15 years.

Vales said that due to the complex nature of the potato genome, generating new cultivars with the right complement of desirable traits is challenging for conventional breeding. Meanwhile, molecular breeding not only has enhanced breeding efficiencies, but also allows addition of a layer of sophistication through gene-editing.

Rathor said the researchers utilised Agrobacterium method to deliver the CRISPR reagents into potatoes because it is reliable, efficient, and least expensive compared to all other delivery methods.

According to the first study, published in the Plant Cell, Tissue and Organ Culture journal, a potato line containing four copies of gfp, which is a jellyfish gene that allows a fluorescence-based visualisation of the gene's activity, was targeted for mutation using the CRISPR-Cas9 system.

The project provided an easy-to-see trait which enabled researchers to optimise the methodology.

Rathore said that the loss of the characteristic green fluorescence and sequencing of the gfp gene following CRISPR treatment indicated that it is possible to disrupt all four copies of the gfp gene. This confirmed that it should be possible to mutate all four alleles of a native gene in the tetraploid potato. Tetraploidy is a condition in which an individual has four copies of each chromosome, instead of two. A tetraploid potato has 48 (12 × 4) chromosomes in each cell. 

The Yukon Gold strain regenerated the best potato cultivar among those considered in the first study. Therefore, this strain was also used in the second study. 

The native gene gbss in the tetraploid Yukon Gold strain was targeted to effectively eliminate amylose. As a result, a potato with starch rich in amylopectin and low in amylose was produced. 

The starch from this potato could be used for industrial purposes, including paper and textile industries. Adhesives or binders, bioplastics, and ethanol could be produced using the starch.

Since the tuber starch has freeze-thaw stability, without the need for chemical modifications, it could also be used to produce frozen foods. Potatoes with amylopectin are the exclusive form of starch, and hence, could be used to produce more ethanol for industrial use or to create alcoholic beverages.

Source: ABP Live

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