Néstor Gutiérrez-Méndez

Assessing the yield, microstructure, and texture properties of miniature Chihuahua-type cheese manufactured with a phospholipase A1 and exopolysaccharide-producing bacteria

Chihuahua cheese or Mennonite cheese is one of the most popular and consumed cheeses in Mexico and by the Hispanic community in the United States. According to local producers the yield of Chihuahua cheese ranges from 9 to 9.5 kg of cheese from 100 kg of milk. Cheese yield is a crucial determinant of profitability in cheese-manufacturing plants; therefore, different methods have been developed to increase it. In this work, a miniature Chihuahua-type cheese model was used to assess the effect of a phospholipase A1 (PL-A1) and exopolysaccharide (EPS)-producing bacteria (separately and in combination) on the yield, microstructure, and texture of cheese. Four different cheeses were manufactured: cheese made with PL-A1, cheese made with EPS-producing bacteria, cheese with both PL-A1 and EPS-producing bacteria, and a cheese control without PL-A1 or EPS-producing bacteria. The compositional analysis of cheese was carried out using methods of AOAC International (Washington, DC). The actual yield and moisture-adjusted yield were calculated for all cheese treatments. Texture profile analyses of cheeses were performed using a texture analyzer. Micrographs were obtained by electron scanning microscopy. Fifty panelists carried out sensorial analysis using ranking tests. Incorporation of EPS-producing bacteria in the manufacture of cheese increased the moisture content and water activity. In contrast, the addition of PL-A1 did not increase fat retention or cheese yield. The use of EPS alone improved the cheese yield by increasing water and fat retention, but also caused a negative effect on the texture and flavor of Chihuahua cheese. The use of EPS-producing bacteria in combination with PL-A1 improved the cheese yield and increased the moisture and fat content. The cheeses with the best flavor and texture were those manufactured with PL-A1 and the cheeses manufactured with the combination of PL-A1 and EPS-producing culture.

Ultraviolet Irradiation Effect on Apple Juice Bioactive Compounds during Shelf Storage

Clarified and standardized apple juice was ultraviolet-irradiated to inactivate polyphenol oxidase enzyme and microbiota, and its effect on bioactive compounds and stability during storage was also evaluated. Apple juice was irradiated with 345.6 J/cm2 and treatment effect was evaluated in terms of color, antioxidant capacity, polyphenol content, pH, titratable acidity and total soluble solids. Using a linear regression design, inactivation kinetic of polyphenol oxidase enzyme was also described. In addition, a repeated measures design was carried out to evaluate apple juice during 24 days of storage at 4 °C and 20 °C. After irradiation, reduction of antioxidant capacity was observed while during storage, ascorbic acid content decreased up to 40% and total polyphenol content remain stable. Ultraviolet irradiation achieved a complete inactivation of polyphenol oxidase enzyme and microbiota, keeping apple juice antioxidants during ultraviolet treatment and storage available until juice consumption. UV-treated apple juice can be used as a regular beverage, ensuring antioxidant intake.

Production of reuterin in a fermented milk product by Lactobacillus reuteri: Inhibition of pathogens, spoilage microorganisms, and lactic acid bacteria

We assessed the antimicrobial activity of reuterin produced in vitro in glycerol aqueous solutions in situ by Lactobacillus reuteri ATCC 53608 as part of a fermented milk product against starter (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus), spoilage (Penicillium expansum), pathogenic (Staphylococcus aureus Salmonella enterica ssp. enterica, and Listeria monocytogenes), and pathogen surrogate (Escherichia coli DH5α) microorganisms. We also assayed the influence of cold storage (28 d at 4°C) and reuterin on the color and rheology of the fermented milk product. We obtained maximum reuterin concentrations of 107.5 and 33.97 mM in glycerol aqueous solution and fermented milk product, respectively. Reuterin was stable throughout its refrigerated shelf life. Gram-positive microorganisms were more resistant to reuterin than gram-negative microorganisms. Penicillium expansum and Lactobacillus reuteri ATCC 53608 survived at concentrations up to 10 and 8.5 mM, respectively. Escherichia coli DH5α was the most sensitive to reuterin (0.9 mM). The presence of reuterin did not cause relevant changes in the quality parameters of the fermented milk product, including pH, acidity, soluble solids, color, and rheological aspects (storage and loss moduli and viscosity). This study demonstrated the viability of using Lactobacillus reuteri ATCC 53608 as a biopreservative in a fermented milk product through reuterin synthesis, without drastically modifying its quality parameters.

Effect of the Addition of Essential Oils and Functional Extractsof Clove on Physicochemical Properties of Chitosan-Based Films

Mechanical and barrier properties of chitosan films prepared with essential oils of clove and functional extract were studied. The films made with functional extracts (esters E6 and E7) presented the significant increment of extensibility compared with the untreated chitosan films. In the case of punction test, the films made with the esters E6 and E7 resisted more the applied strength before tearing up compared with the chitosan control film (without any treatment). Thermogravimetric analysis values were determined for the chitosan control film and chitosan film treated with clove essential oil obtaining 112.17°C and 176.73°C, respectively. Atomic force microscopy (AFM) was used to determine their morphology by analyzing their surfaces and phase arrangement; AFM was also used to observe the porosity in chitosan-based antimicrobial films and the chitosan films incorporating functional extracts. The water vapour permeability (WVP) data showed that incorporating the functional extract to the formulation of films has a positive effect on water vapour barrier properties. In general, the incorporation of essential oils and functional extract of clove at 20% in chitosan films caused microstructural changes that were dependent on the different affinity of components.

Partial characterization of a plant coagulant obtained from the berries of Solanum elaeagnifolium

The berries of Solanum elaeagnifolium (trompillo) have been used since ancient time in Chihuahua, Mexico, as a milk coagulant in cheese making. This article describes an approach to the characterization of the plant coagulant from trompillo. From the main results, it was noticed that only the yellow berries of trompillo have proteolytic and milk-clotting activity. These activities were observed in the crude extracts (CEs) obtained from both seeds and fruit peels of yellow berries. The proteolytic activities of these CEs ranged from 6.0 to 8.5 U-Gly/mg, although the absence of NaCl in the CEs decreased their activities significantly. The milk-clotting activities of CEs from the berries of trompillo (4347–2564 MCA) were similar to those reported for other plant coagulants. Some CEs had a similar ratio of milk-clotting activity/proteolysis as rennin and chymosin. This plant coagulant produced an unspecific hydrolysis on caseins, increasing the yield in fresh-type miniature cheese.

Short communication: Potential of Fresco-style cheese whey as a source of protein fractions with antioxidant and angiotensin-I-converting enzyme inhibitory activities

Recently, traditional Mexican Fresco-style cheese production has been increasing, and the volume of cheese whey generated represents a problem. In this study, we investigated the chemical composition of Fresco-style cheese wheys and their potential as a source of protein fractions with antioxidant and angiotensin-I-converting enzyme (ACE)-inhibitory activities. Three samples from Fresco, Panela, and Ranchero cheeses whey were physicochemically characterized. Water-soluble extracts were fractionated to obtain whey fractions with different molecular weights: 10-5, 5-3, 3-1 and <1 kDa. The results indicated differences in the lactose, protein, ash, and dry matter contents (% wt/wt) in the different Fresco-style cheese wheys. All whey fractions had antioxidant and ACE-inhibitory activities. The 10-5 kDa whey fraction of Ranchero cheese had the highest Trolox equivalent antioxidant capacity (0.62 ± 0.00 mM), and the 3-1 kDa Panela and Fresco cheese whey fractions showed the highest ACE-inhibitory activity (0.57 ± 0.02 and 0.59 ± 0.04 μg/mL 50%-inhibitory concentration values, respectively). These results suggest that Fresco-style cheese wheys may be a source of protein fractions with bioactivity, and thus could be useful ingredients in the manufacture of functional foods with increased nutritional value.

Ultrasound-assisted crystallization of lactose in the presence of whey proteins and κ-carrageenan

The conventional process of lactose crystallization is prolonged, hardly controllable and the crystals have low quality. In this work, the effect of ultrasound on the crystallization of lactose in an aqueous system was assessed. Additionally, it was studied how the presence of whey proteins (which are a common impurity) and κ-carrageenan (that possess high water-binding capacity) could modify the process of lactose crystallization. Lactose solutions at 25% were sonicated in a continuous flow chamber at two different energy densities (9 and 50 J mL-1) before the start of crystallization. Some of these lactose solutions were previously added with κ-carrageenan (0, 150 and 300 mg L-1), with whey proteins (0.64%) or with both at the same time. Ultrasound sped up the rate of crystallization, decreased the crystals size and narrowed the crystal size distribution (CSD). The presence of whey proteins accelerated the process of crystallization but induced the formation of amorphous lactose. Likewise, the rate of lactose crystallization was improved by the addition of 150 mg L-1 of carrageenan. Whereas, the combination of carrageenan and whey proteins generated the smallest crystals (6 μm), the narrowest CSD and minimized the formation of amorphous lactose.

Seasonal influence on the microbial profile of Chihuahua cheese manufactured from raw milk

Samples of artisanal Chihuahua cheese were collected in autumn, winter and summer from five farms from Chihuahua State, Mexico; temperature, pH and processing times were also recorded. Indicator microorganisms as well as lactic acid bacteria were determined. Samples were negative for Salmonella sp., and, except for coliforms, the particular season had a strong effect on counts of all microorganisms (4.8–6.0 log10 cfu/mL Staphylococcus aureus; 6.3–7.3 log10 cfu/mL presumptive Lactococcus sp; 7.3–8.0 log10 cfu/mL presumptive mesophilic lactobacilli), as well as on processing conditions. The information presented is aimed to characterise Chihuahua cheese as a traditional product.

Improving Cull Cow Meat Quality Using Vacuum Impregnation

Boneless strip loins from mature cows (50 to 70 months of age) were vacuum impregnated (VI) with an isotonic solution (IS) of sodium chloride. This study sought to determine the vacuum impregnation and microstructural properties of meat from cull cows. The experiments were conducted by varying the pressure, p1 (20.3, 71.1 kPa), and time, t1 (0.5, 2.0, 4.0 h), of impregnation. After the VI step, the meat was kept for a time, t2 (0.0, 0.5, 2.0, 4.0 h), in the IS under atmospheric pressure. The microstructural changes, impregnation, deformation, and porosity of the meat were measured in all the treatments. Impregnation and deformation levels in terms of volume fractions of the initial sample at the end of the vacuum step and the VI processes were calculated according to the mathematical model for deformation-relaxation and hydrodynamic mechanisms. Scanning electron microscopy (SEM) was used to study the microstructure of the vacuum-impregnated meat samples. Results showed that both the vacuum and atmospheric pressures generated a positive impregnation and deformation. The highest values of impregnation X (10.5%) and deformation γ (9.3%) were obtained at p1 of 71.1 kPa and t1 of 4.0 h. The sample effective porosity (εe) exhibited a significant interaction (p < 0.01) between p1×t1. The highest εe (14.0%) was achieved at p1 of 20.3 kPa and t1 of 4.0 h, whereas the most extended distension of meat fibers (98 μm) was observed at the highest levels of p1, t1, and t2. These results indicate that meat from mature cows can undergo a vacuum-wetting process successfully, with an IS of sodium chloride to improve its quality.

Partial Characterization of Bacteriocin Produced by Halotolerant Pediococcus acidilactici Strain QC38 Isolated from Traditional Cotija Cheese

During a screening of lactic acid bacteria producing bacteriocin from Cotija cheese, the strain QC38 was isolated. Based on the 16S rRNA gene nucleotide sequencing (516 pb accession no KJ210322) and phylogenetic analysis, the isolate was identified as Pediococcus acidilactici. Neutralized cell-free supernatant was tested for antimicrobial activity against 17 Gram-negative and Gram-positive pathogens. Growth inhibition was achieved against Listeria monocytogenes (supplier or indication or source), Staphylococcus aureus, Vibrio vulnificus, Vibrio cholerae O1 Ogawa, Vibrio cholerae NO 01 and Salmonella enterica subsp. Enterica serovar Typhimurium. Bacteriocin-like substance, after heating at 121°C for 15 min it remained stable and its antimicrobial activity was observed at pH ranging from 1.0 to 10.0 but inactivated by α-chymotrypsin and proteinase K. Strain QC38 was able to grow in 1-9% NaCl concentration. The plate overlay assay showed an approximate size of bacteriocin-like substance between 3.4 and 6.5 kDa. P. acidilactici QC38 harboured a plasmid that contains a gene for a pediocin (PA-1).