Structure and stability of the potato cysteine protease inhibitor group (cv. Elkana)

Physical, Chemical and Biochemical Modification Approaches of Potato (Peel) Constituents for Bio-Based Food Packaging Concepts: A Review

Potatoes are grown in large quantities and are mainly used as food or animal feed. Potato processing generates a large amount of side streams, which are currently low value by-products of the potato processing industry. The utilization of the potato peel side stream and other potato residues is also becoming increasingly important from a sustainability point of view. Individual constituents of potato peel or complete potato tubers can for instance be used for application in other products such as bio-based food packaging. Prior using constituents for specific applications, their properties and characteristics need to be known and understood. This article extensively reviews the scientific literature about physical, chemical, and biochemical modification of potato constituents. Besides short explanations about the modification techniques, extensive summaries of the results from scientific articles are outlined focusing on the main constituents of potatoes, namely potato starch and potato protein. The effects of the different modification techniques are qualitatively interpreted in tables to obtain a condensed overview about the influence of different modification techniques on the potato constituents. Overall, this article provides an up-to-date and comprehensive overview of the possibilities and implications of modifying potato components for potential further valorization in, e.g., bio-based food packaging.

A comprehensive study on structures and characterizations of 7S protein treated by high intensity ultrasound at different pH and ionic strengths

High intensity ultrasound (HIU) effects on soy 7S proteins in various pH (pH = 3.0 and 7.0) and ionic strengths (I = 0.1, 0.3 and 0.5) were investigated. When dissolved in pH = 7.0, the 7S proteins formed aggregates at the low ionic strength (I = 0.1), while large aggregates were dissociated as the ionic strengths increased (I = 0.3 or 0.5) after HIU treatments. Moreover, the 7S proteins were unfolded at I = 0.3 and I = 0.5 through HIU. When dissolved in pH = 3.0, the 7S proteins were extensively positively charged, which favored the HIU-induced denaturation of the proteins. When the ionic strengths were increased, the larger aggregates of the proteins were found after HIU. The electrostatic screening from the ions was essential for the unfolding/refolding and aggregating behavior of the HIU proteins, which was also proved from the structural measurements. The current study illustrated that environmental factors were of great importance for the HIU effects on food protein functionalities.

Influence of pH, Temperature and Protease Inhibitors on Kinetics and Mechanism of Thermally Induced Aggregation of Potato Proteins

Understanding aggregation in food protein systems is essential to control processes ranging from the stabilization of colloidal dispersions to the formation of macroscopic gels. Patatin rich potato protein isolates (PPI) have promising techno-functionality as alternatives to established proteins from egg white or milk. In this work, the influence of pH and temperature on the kinetics of PPI denaturation and aggregation was investigated as an option for targeted functionalization. At a slightly acidic pH, rates of denaturation and aggregation of the globular patatin in PPI were fast. These aggregates were shown to possess a low amount of disulfide bonds and a high amount of exposed hydrophobic amino acids (S₀). Gradually increasing the pH slowed down the rate of denaturation and aggregation and alkaline pH levels led to an increased formation of disulfide bonds within these aggregates, whereas S₀ was reduced. Aggregation below denaturation temperature (T_d) favored aggregation driven by disulfide bridge formation. Aggregation above T_d led to fast unfolding, and initial aggregation was less determined by disulfide bridge formation. Inter-molecular disulfide formation occurred during extended heating times. Blocking different protein interactions revealed that the formation of disulfide bond linked aggregation is preceded by the formation of non-covalent bonds. Overall, the results help to control the kinetics, morphology, and interactions of potato protein aggregation for potential applications in food systems.

Cysteine Protease Inhibitors Reduce Enzymatic Browning of Potato by Lowering the Accumulation of Free Amino Acids

Enzymatic browning is a major issue affecting the quality of processed potato (Solanum tuberosum L.). To understand the molecular mechanism of browning, transcriptional analyses were performed by employing potatoes that differed in browning. Coexpression analysis indicated that 9 out of 15 upregulated genes in browning-less groups encoded for potato protease inhibitors (StPIs). In addition, gene otology analysis showed that the enriched terms were mainly involved in protease inhibitors. Overexpression of cysteine StPI 143 and StPI 146 individually reduced browning and lowered protease activities and tyrosine and total free amino acid (FAA) contents, but they could not decrease polyphenol oxidase activity. Moreover, supplementing exogenous tyrosine or total FAAs into transgenic potato mash to wild-type amounts promoted mash browning, browning with total FAAs, more than with tyrosine, resembling wild-type levels. These results implied that cysteine StPIs reduced browning via lowering the accumulation of FAAs in addition to tyrosine. Our findings have enriched the knowledge about the roles and mechanisms of protease inhibitors in regulating enzymatic browning of potato, which provide new ways for controlling potato browning.

A Simple Method to Prepare Raw Dehydrated Potato Flour by Low-Temperature Vacuum Drying

A simple method called low-temperature vacuum drying (LTVD) was used to produce a novel dehydrated potato flour called raw dehydrated potato flour (RDPF). Preparing RDPF by LTVD at 60°C, 70°C and 80°C in both slice and dice shape was investigated. Potato samples in dice shape are easier dehydrating than in slice shape, the starch granules of RDPF maintain ellipsoid shape as the native potato starch. The best temperature of LTVD to prepare the RDPF is around 70°C according to CIE chromaticity results. Dehydrate at 60°C in dice shape, 88.37% of the trypsin inhibitor activity of the fresh potato is maintained. The Mixolab curve shows that the RDPF has some similar rheological properties of the wheat flour. Protein undenatured, starch ungelatinized, with the high performance of processing properties, RDPF has a number of potential applications in the potato staple food manufacture.

Teaching Enzyme Activity to the Visual Impaired and Blind Students

Biochemistry requires a high abstraction level, and different approaches should be used to enable the proper understanding of different subjects. In particular, students with visual impairment or blindness need special attention, not due to a lack of cognitive skills, but due to the fact that most of the teaching methods are visual. Enzyme properties are usually taught through experimental data that show how the activity changes in different conditions, which end up with the analysis of graphs. Therefore, our group developed experiments and graphical representations that enable visually impaired and blind students to understand enzyme properties. The experiments were done with pineapple bromelain, using reconstituted dry milk and gelatin as substrates. The “visualization” of the results were based on the sensation of the viscosity of the samples. The graphs were made with cold porcelain with all the labels (legends and numbers) written in Braille with a positive slate. From our experience with a blind student, both the experiments and the graphic representations were useful adaptations for teaching enzyme properties.

Contact Urticaria to Raw Potato and Lentil Anaphylaxis: A Case Report

Potatoes and lentils are highly consumed throughout the world. Adverse reactions to potatoes among children are considered uncommon and usually result from ingestion. Allergy to raw potato has mainly been described in adults, usually in the form of oral-contact dermatitis or contact urticaria, but also may manifest as asthma, rhinoconjunctivitis, wheezing, or even anaphylaxis. Lentils, chickpeas, beans, and peas are the most commonly consumed legumes in Turkey and the Mediterranean region. In the literature, type I hypersensitivity to lentils and legumes is rare. We report a case of a 16-month-old boy with both urticaria induced by raw potato and lentil-induced anaphylaxis.

Molecular cloning and biochemical characterization of a novel cystatin from Hevea rubber latex

A novel cDNA encoding a cysteine proteinase inhibitor or phytocystatin was isolated from Hevea brasiliensis RRIM600 rubber latex cDNA library. The full-length HbCPI obtained from rapid amplification of cDNA ends contains 588 bp. An open reading frame of 306 bp encodes for a protein of 101 amino acids with the typical inhibitory motifs of phytocystatin superfamily, namely the central signature motif QXVXG, a GG doublet and LARFAV-like motifs in the N-terminal part, and conserved A/PW residues in the C-terminal region. Sequence comparison showed that the deduced amino acid sequence was similar to that of cysteine protease inhibitor from Manihot esculenta (84% identity). The HbCPI was subcloned into expression vector pQE-40 and then overexpressed in Escherichia coli M15 strain (pREP4) as a His-tagged recombinant protein with molecular mass approximately 13 kDa. The purified HbCPI showed thermal stable property and efficiently inhibited the protease activity of papain by non-competitive inhibition with K(i) value of 15.4 nM. Beside latex, HbCPI also transcripted in leaf and young seed. The HbCPI message accumulation was induced by phytopathogenic fungi Phytophthora palmivora infection. These data suggest that HbCPI might play crucial roles in defense mechanism against biotic stimuli.

Conformational studies on Arabidopsis sulfurtransferase AtStr1 with spectroscopic methods

Sulfurtransferases/rhodaneses (Str) are enzymes widely distributed in archaea, prokaryota and eukaryota, and catalyze the transfer of sulfur from a donor molecule to a thiophilic acceptor substrate. In this reaction, Str cycles between the sulfur-free and the sulfur-substituted form. Two-domain Str consist of two globular domains of nearly identical size and conformation connected by a short linker sequence, which is elongated in plant two-domain Str proteins compared to Str in other organisms. The two-domainArabidopsis thalianaStr1 protein (At1g79230) was expressed inEscherichia colias a mature protein, as a variant without the elongated linker sequence, and as AtStr1C332S and AtStr1C339V. The persulfuration state of the purified recombinant proteins was investigated in the presence and absence of sulfur donors by fluorescence spectroscopy. The secondary structure was analyzed by circular dichroism (CD) in the far-UV range, while overall changes in tertiary structure were determined by CD in the near-UV range. Finally, protein stability was analyzed by tryptic digestion. The elongated linker sequence is essential for correct conformation and stability, and thereby affects the catalytic activity of AtStr1. Replacement of the catalytic cysteine residue C332 leads to higher rigidity of the molecule, whereas replacement of C339 does not lead to any conformational changes, providing evidence of the direct involvement of C339 in catalysis.