Vrani Ibarra-Junquera

Antioxidant activity and content of chlorophylls and carotenoids in raw and heat-processed Jalapeño peppers at intermediate stages of ripening.

Jalapeño peppers at intermediate ripening stages (IRS) are typically discarded at the packinghouse because they are not demanded for fresh consumption or industrial processing. These peppers have been scarcely studied in terms of pigment composition and bioactivity. In this study, the profile of pigments (carotenoids and chlorophylls) and antioxidant activity were determined in raw and heat-processed Jalapeño peppers at three IRS (brown, 50% red, and 75% red). Peppers contained 64 different pigments. Chlorophylls were the most abundant pigments in raw brown peppers while capsanthin was the most abundant at the other IRS. The content of most pigments decreased due to heat treatments. Several pheophytins and cis isomers of carotenoids were generated by heat processing. Boiling and grilling consistently decreased and increased the antioxidant activity of peppers, respectively. Tested peppers showed a more complex/abundant pigment content and higher antioxidant activity than those typically reported for green and red peppers.

Method to concentrate protein solutions based on dialysis-freezing-centrifugation: enzyme applications.

One of the recurrent methodological problems in preparative biochemical work is the concentration of dilute protein solutions, including culture supernatants resulting from biotechnological processes. A procedure was developed to concentrate enzymes by a novel cryoconcentration system. This approach includes a new device that facilitates the sample freezing and the subsequent solute elution from the frozen matrix by centrifugation. The optimal centrifugation conditions for this cryoconcentration system were obtained using whey protein solution as a model. The procedure was applied to concentrate dilute solutions of commercial pectinase, measuring the endopolygalacturonase (EPG) activity of this enzyme in the concentrate by a method based on the on-line torque measurement, and of recombinant fructan:fructan 1-fructosyltransferase (1-FFT) protein of Pichia pastoris from a culture in a bioreactor, as an expression system. The optimal centrifugation speed, time, and temperature were 6150 g, 20 min, and 4 °C, respectively. The concentration factors for the dilute protein solutions were 9.2-, 11.2-, and 17.1-fold for 1-FFT, whey, and commercial pectinase, respectively. Recoveries ranged from 87% to 93%. The procedure allowed concentrating proteins efficiently without affecting their enzymatic activity.

Effect of heat processing on the profile of pigments and antioxidant capacity of green and red jalapeño peppers.

Raw and heat-processed jalapeño peppers (green and red) were evaluated for their pigment profile and antioxidant capacity. Sixty-seven pigments were separated and characterized by HPLC-DAD-MS, including carotenoids (isomers and esters), chlorophylls, and pheophytins. The distinctive characteristics of this pepper genotype were the presence of antheraxanthin monoesters, zeaxanthin monoesters, mutatoxanthin diesters, and a higher content of free capsanthin relative to the mono- and diesterified forms. Chlorophyll a and free all-trans-lutein were the major pigments in raw green peppers, whereas free all-trans-capsanthin was the most abundant pigment in raw red peppers. Twelve compounds were generated by the heat treatments, mainly pheophytins and cis isomers of carotenoids. Heat treatments affected differentially the concentration of individual pigments. Red peppers showed a higher antioxidant capacity than green fruits. Heating caused minor changes in the antioxidant capacity of peppers.

Online monitoring of Mezcal fermentation based on redox potential measurements

We describe an algorithm for the continuous monitoring of the biomass and ethanol concentrations as well as the growth rate in the Mezcal fermentation process. The algorithm performs its task having available only the online measurements of the redox potential. The procedure combines an artificial neural network (ANN) that relates the redox potential to the ethanol and biomass concentrations with a nonlinear observer-based algorithm that uses the ANN biomass estimations to infer the growth rate of this fermentation process. The results show that the redox potential is a valuable indicator of the metabolic activity of the microorganisms during Mezcal fermentation. In addition, the estimated growth rate can be considered as a direct evidence of the presence of mixed culture growth in the process. Usually, mixtures of microorganisms could be intuitively clear in this kind of processes; however, the total biomass data do not provide definite evidence by themselves. In this paper, the detailed design of the software sensor as well as its experimental application is presented at the laboratory level.

Effect of ripening and heat processing on the physicochemical and rheological properties of pepper pectins.

Water-, chelator-, and alkali-soluble pectins were isolated from raw and heat-processed Jalapeño peppers (green and red) and their physiochemical and rheological properties were determined. The yield, tristimulus color, degree of methyl esterification, monosaccharide composition, molecular weights distribution, and protein content depended on ripening and heat processing. The viscosity properties of pectins were independent of ripening. The water-soluble pectin was the most abundant pectin. Pectins from grilled peppers showed the lowest L* values. The alkali-soluble pectin showed the highest protein content. The content of xylose, rhamnose, and mannose in pectins was highly altered by tested factors. The degree of methyl esterification of pectins ranged from 26.8 to 91.6%. The peak Mw of the main fraction of tested pectins was sequentially reduced by ripening and heat processing. Pectins from raw peppers showed the best viscosity properties.

Improving sodium dodecyl sulfate polyacrylamide gel electrophoresis detection of low-abundance protein samples by rapid freeze centrifugation.

This work presents a rapid and simple freeze centrifugation method to concentrate dilute protein solutions for detection by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) Coomassie blue staining. Moreover, a simple way to assemble a cryoconcentration device is presented, and its use is discussed. Commercial purified protein standard and an enzyme with high fructosyltransferase (FTase) activity, coming from target fractions obtained by chromatographic separation, were used as an example. FTase, coming directly from the chromatographic fractions, was difficult to view through SDS-PAGE analysis; however, it was easily visualized, and its activity was enhanced, after the application of the freeze centrifugation protocol presented here.

Effects of pectin on lipid digestion and possible implications for carotenoid bioavailability during pre-absorptive stages: A review

Pectin, an abundant polysaccharide in the human diet, has structural characteristics and functional properties that are strongly dependent on the food matrix (e.g., origin, type, cultivar/variety, ripening stage, style and intensity of processing). These polysaccharides have a strong effect on lipid digestion, which is required for the liberation of carotenoids from emulsified lipid droplets in the gastrointestinal content and for the formation of micelles, in which the carotenoids must be incorporated before absorption. Only micellarized carotenoids can be absorbed and subsequently exert protective effects on human health. The alteration of lipolysis by pectin can occur through several mechanisms; however, they have not been linked directly to carotenoid micellarization. This paper provides an overview of the effects of the properties of pectin on the ion concentration in the digestive content, the viscosity of the digestive medium, the properties of the lipid droplet surfaces and lipase activity and analyzes the impact of these events on lipid digestion and subsequent carotenoid micellarization.

PI-controlled bioreactor as a generalized Liénard system

Abstract It is shown that periodic orbits can emerge in Cholette’s bioreactor model working under the influence of a PI-controller. We find a diffeomorphic coordinate transformation that turns this controlled enzymatic reaction system into a generalized Lienard form. Furthermore, we give sufficient conditions for the existence and uniqueness of limit cycles in the new coordinates. We also perform numerical simulations illustrating the possibility of the existence of a local center (period annulus). A result with possible practical applications is that the oscillation frequency is a function of the integral control gain parameter.

Evaluation of the Freezing and Thawing Cryoconcentration Process on Bioactive Compounds Present in Banana Juice from Three Different Cultivars

Abstract In this research, we produced concentrates of banana juices from three different cultivars of bananas (Enano gigante and two hybrids FHIA-17 and FHIA-23) by the freezing and thawing method. To track the cryoconcentration process, different parameters were monitored in the melted fractions, such as variation of the content of soluble solids, concentration of polyphenols (Folin–Ciocalteu), reducing sugar (DNS assay), minerals (K, Mg, Ca, P, Na, Mn, Cu and B) by inductively coupled plasma-optical emission spectroscopy and the main volatile compounds by headspace-GC–MS. It was found that the solution obtained during thawing showed higher concentrations than the original solution. The concentrations of polyphenols were duplicated in FHIA-17 cultivar (758.53 mg/100 ml), and the concentrates obtained in this study proved to be good sources of K and Mg 5,054.6 mg/l and 485.4 mg/l with around 70% and 40% of the recommended daily intake (RDI), respectively. In addition, the concentrates contained a very low level of Na around 1% of the RDI. Furthermore, the cryoconcentration process of the bioactive compounds presented a sigmoid behavior, and the inflexion point in the function was proposed as stop point of the process. Finally, the main volatile compounds reported as responsible for the banana aroma were identified, and its cryoconcentration proved. These results suggest that consumption of banana juice concentrates obtained by the freezing and thawing method can provide bioactive compounds needed for health.

The effect of ripening, heat processing and frozen storage on the in vitro bioaccessibility of capsaicin and dihydrocapsaicin from Jalapeño peppers in absence and presence of two dietary fat types

To date, there is no information in the literature regarding the bioaccessibility of capsaicinoids from natural sources. The effect of ripening and heat-processing on the in vitro bioaccessibility of capsaicin and dihydrocapsaicin was studied in the absence and presence of two dietary fat types. The capsaicinoid bioaccessibility was also studied during the frozen storage of peppers for 6 months. Fresh green peppers showed the highest capsaicinoid bioaccessibility, as compared with that of other experimental groups. The bioaccessibility of capsaicinoids from green peppers decreased as the intensity of heat treatment increased. The dietary fat increased the bioaccessibility of capsaicin and dihydrocapsaicin in digestions with red peppers, especially that of dihydrocapsaicin. The bioaccessibility of capsaicinoids was altered by frozen storage. The Caco-2 cells incorporated capsaicin and dihydrocapsaicin (8.4% and 10.9%, respectively) but they were probably metabolized by cells.