Relationship of Compositional, Mechanical, and Textural Properties of Gluten-Free Pasta Using Different Quinoa (Chenopodium quinoa) Varieties.

Quinoa epitomizes the drive for healthier foods with ethnic concepts in developed countries, particularly among millennials. As a result, the popularity of quinoa as a gluten-free alternative has steadily grown over the last 20 years. Despite this, little is known about the impact of specific varieties on processed foods. The purpose of this study was to examine the impact of quinoa varieties (variety and content) on the mechanical and textural properties of buckwheat-based extruded pasta (spaghetti). Peruvian native (var. rosada taraco, kuchivila, negra collana, and mistura) and Latvian-grown (var. titicaca) varieties were independently incorporated to pasta between 5 and 20% (w/w). Pasta containing 20% quinoa var. negra collana, which presented the largest content of fiber and lowest content of saponin, was strongly associated to structural resilience (i.e., cohesiveness, firmness). Conversely, pasta containing 20% quinoa var. Titicaca appeared structurally weak (i.e., smooth). The addition of saponin-containing varieties to pasta (20%), such as rosada taraco and mistura, resulted in resilient structures with little effect on taste (incl. bitterness). Despite initial stability, pasta containing 20% quinoa var. kuchivila suffered heavy structural damage. In conclusion, the relationship of compositional, mechanical, and textural properties of pasta was strongly variety-dependent.

Protein-lipid co-oxidation in emulsions stabilized by microwave-treated and conventional thermal-treated faba bean proteins.

The course of protein-lipid co-oxidation was investigated in oil-in-water emulsions stabilized with proteins extracted from microwave-treated (MWT) and conventional thermal-treated (CTT) faba beans stored at 37°C for 7 days. Emulsions prepared with proteins from untreated (UT) faba beans and soy protein isolate (SP) were monitored for comparison. Lipid oxidation was detected through formation of primary and secondary oxidation products while protein oxidation was examined via tryptophan fluorescence degradation in interface and aqueous phase. Oxidation of proteins was more emphasized in the interfacial layers of MWT, CTT, and SP emulsions than in UT emulsions due to the prominence of radical chain-driven co-oxidation mechanism while lipoxygenase (LOX) activity in UT and MWT emulsions resulted in high amounts of hydroperoxides and abundance in lipid oxidation volatiles. Conventional thermal treatment provided better oxidative stability than microwave treatment reflected in lower levels of hydroperoxides and relative lack of diversity in lipid volatiles. Among detected volatiles, formation of ketones was more distinguished in MWT, CTT, and SP emulsions while UT emulsions contained a more diverse range of alkenals and alkanals. Ketones are known to form mainly through radical recombination reactions which combined with the results of protein oxidation supports that radical transfer reactions between proteins and lipids were the driving force behind oxidation in MWT, CTT, and SP emulsions. Treatments of faba beans resulted in increased oxidative stability of emulsified lipids and lower degradation of aqueous phase proteins.

Tryptophan and Cysteine Oxidation Products Dominate in α-Lactalbumin-Derived Peptides Analyzed with LC-MSn.

α-Lactalbumin (α-La), a major milk whey protein, is comprised of several amino acids prone to metal-catalyzed oxidation (MCO) typical in processing and during storage of foods. New tools are needed for the detection of characteristic oxidation products especially from tryptophan and cysteine that often remain unrecognized when using the traditional methods of carbonyl formation monitoring. In this study, the oxidative changes in α-La were investigated through tryptic digestion and collection of 3 descriptive peptides fitted into a metal-catalyzed oxidation (Fenton reaction) model. The peptide samples were oxidized at +37 °C for 14 d and explored with liquid chromatography-quadrupole ion trap-mass spectrometer (LC-MSn ). The fractionated α-La peptides were valyl-glycyl-isoleucyl-asparaginyl-tyrosyl-tryptophyl-leucyl-alanyl-histidyl-lysine (VGINYWLAHK), leucyl-aspartyl-glutaminyl-tryptophyl-leucyl-cysteinyl-glutamyl-lysine (LDQWLCEK), and tryptophyl+16 -leucyl-alanyl-histidyl-lysyl-alanyl-leucyl-cysteine (W+16 LAHKALC). Oxidation of several amino acids, such as cysteine, histidine, lysine, and tryptophan was observed. In the peptide LDQWLCEK, cysteine was rapidly trioxidized to sulfonic acid, followed by other amino acid side chains as secondary oxidation sites. Tryptophan oxidation was more pronounced in the peptides W+16 LAHKALC and VGINYWLAHK, and also formation of the harmful N-formylkynurenine was observed. As a conclusion, several stable and promising oxidation markers are proposed for α-La, which could be implemented in the evaluation of quality and safety of dairy protein-containing products.

LC-MS investigations on interactions between isolated ß-lactoglobulin peptides and lipid oxidation product malondialdehyde.

Interactions between secondary lipid oxidation product malondialdehyde (MDA) and selected ß-lactoglobulin (ß-Lg) peptides were investigated. Selected tryptic peptides of ß-Lg (ALPMHIR, LIVTQTMK and VLVLDTDYK) were fractionated via preparative-HPLC and incubated with MDA at 37°C and 60°C for 7 days. Changes in samples were monitored with LC-ESI-MS coupled with UV and fluorescence detectors. Prominent modifications in peptide samples included formation of two distinct types of MDA adducts observed with mass increments of 54 and 134 amu, corresponding to Schiff base and dihydropyridine (DHP)-type adducts, respectively. Modified peptides with m/z +54 amu were more stable at 37°C than at 60°C but showed more rapid formation than compounds with m/z +134 amu. MDA-peptide adducts resulting in +134 amu mass increment displayed strong fluorescent characteristics and they were more stable than Schiff base adducts at 60°C.

A novel LC-MS application to investigate oxidation of peptides isolated from ß-lactoglobulin.

Oxidation of ß-lactoglobulin (ß-Lg), a typical milk whey protein, was investigated by oxidizing its three tryptic peptides after separation and fractionation by preparative HPLC. Oxidation was performed with H2O2 and Fe(3+) in piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES) buffer containing ascorbic acid, by keeping the samples in an oven of +37 °C for 14 days. Changes in the oxidized peptides were then analyzed with LC-ESI-QIT-MS. The peptides chosen were Ala-Leu-Pro-Met-His-Ile-Arg (ALPMHIR), Leu-Ile-Val-Thr-Gln-Thr-Met-Lys (LIVTQTMK) and Val-Leu-Val-Leu-Asp-Thr-Asp-Tyr-Lys (VLVLDTDYK), all containing amino acids of oxidative interest. Especially methionine (M) was prone to oxidize as well as dioxidize, along with tyrosine (Y), histidine (H) and/or proline (P). The ions m/z 854 [ALPMHIR + O], m/z 950 [LIVTQTMK + O] and m/z 966 [LIVTQTMK + 2O] are considered very promising indicators of ß-Lg oxidation. Consequently, this study proposes a novel approach in peptide oxidation research through monitoring the oxidation markers identified with the LC-MS(n).