Effect of Fat Type on Starch and Protein ... - Wiley Online Library

RESEARCH ARTICLE Starch and Protein Digestibility

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Effect of Fat Type on Starch and Protein Digestibility of Traditional Tamales María Eva Rodríguez-Huezo, Pamela Flores-Silva, Samuel Garcia-Diaz, Monica Meraz, Eduardo Jaime Vernon-Carter, and Jose Alvarez-Ramirez* maize husks or green plantain leaves, which are wrapped to form cylindrical, rectangular or square-like packages of differing sizes. Tamales can be filled with meats, cheeses, fruits, vegetables, chilies or any preparation according to taste. Finally, tamales are steam cooked at 90–100 C for about 1–2 h. Tamales are from pre-Columbian origin, and the Aztec and Maya civilizations, as well as the Olmeca and Tolteca before them, used tamales as easily portable food, for hunting trips, and for traveling large distances, as well as supporting their armies.[2] Tamales were also considered sacred as it is the food of the gods, so tamales played a large part in their rituals and festivals of these cultures.[3] Tamales became one of the representatives of Mexican culinary tradition in Europe, as the Spanish conquistadors took them back to Spain as proof of civilization.[4] Tamales are extensively consumed in Central and South America, the Caribbean, USA and as far as the Philippines and Guam, the latter probably due to the galleon trade that occurred between the ports of Manila and Acapulco. Gross estimates by the authors suggest that about 10 million tamales of 90 g each are daily consumed in Mexico City alone. Tamales represent an important energy source for consumers, but can also contribute to the increased risk of diseases linked to the metabolic syndrome, particularly in urban populations.[5] In this regard, an accurate characterization of the digestibility of traditional products like tamales can provide valuable information for their re-formulation into “healthier” products with higher fiber content. As occurs with many traditional foods, there are very few systematic studies regarding the physicochemical transformations undergone by tamales during their production.

Tamales are Mexican traditional food consisting of a mixture of nixtamalized maize flour, fat, and water, kneaded into batter (masa). Energy consumed in excess of an individualś requirements can contribute to the development of overweight and obesity, and to the risk of developing metabolic syndrome. There is a drive to improve the “healthiness” of traditional foods such as tamales. In turn, this motivates the need of evaluating the physicochemical transformations occurring during tamales preparation. This work studies the effect of using pork lard (AF) and hydrogenated vegetable shortening (VF) on the physicochemical properties and digestibility of tamales, as both type of fats are used in artisanal and mechanized production. VF imparts better viscoelastic properties to masa and better textural properties to tamales than AF. Both types of fat participate in the formation of amylose-lipid inclusion complexes, but higher resistant starch (RS) contents occur with VF than for AF, and are reflected in lower digestibility rates. An increase in readily digestible starch fraction is also detected, and is of about 40% when using AF. Both fats negatively effect the digestibility of protein. The results show that the fat type determines the digestibility properties of tamales.

1. Introduction Tamal (Plural: tamales, from the Nahuatl etymology tamalli, meaning wrapped[1] refers to a traditional food prepared with nixtamalized maize flour, animal fat, and salt. In a first step, these three ingredients are blended manually to form batter (a.k.a., masa). Subsequently, masa portions are spread on soaked Dr. M. E. Rodríguez-Huezo Departamento de Ingeniería Química y Bioquímica Tecnol ogico de Estudios Superiores de Ecatepec Av. Tecnol ogico s/n esq. Av. Central, Ecatepec EDOMEX 55210, Mexico Dr. P. Flores-Silva, Dr. E. J. Vernon-Carter, Dr. J. Alvarez-Ramirez Departamento de Ingeniería de Procesos e Hidráulica Universidad Aut onoma Metropolitana-Iztapalapa. Iztapalapa CDMX 09340, Mexico E-mail: [email protected] S. Garcia-Diaz, Dr. M. Meraz Departamento de Biotecnología Universidad Aut onoma Metropolitana-Iztapalapa. Iztapalapa CDMX 09340, Mexico The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/star.201700286.

DOI: 10.1002/star.201700286

Starch - Stärke 2018, 1700286

Cooking of tamales is carried out under boiling conditions (90–100 C) at relatively high humidity conditions (70%). Although nixtamalized maize flour is used for preparing tamales, the additional steam cooking is likely to induce further transformations that may affect pasting, morphological, crystalline, thermal, and physicochemical properties, as well as enzymatic and acid susceptibility of starch.[6] On the other hand, heating of aqueous starch-fat blends may produce amylose-lipid complexes,[7] a type of amylose-inclusion arrangements that are resistant to the action of digestive enzymes.[8]

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Figueroa-Cárdenas et al.[9] found that masa made from maize grains with different endosperm types (hard, soft, and very soft) and hydrogenated vegetable shortening, cooked at boiling temperatures (>90 C for 2 h) produced amylose-lipid complexes which increased resistant starch content (RS), and lowered the digestibility rate. Mariscal-Moreno et al.[10] reported that RS in tamales increased 1.6–3.7-fold compared to that contained in native maize starch. During centuries, the artisanal preparation of tamales in Prehispanic Mexico used animal fat (AF) from several sources including turkey, deer, and mainly poultry (37% of saturated fat and 28% of unsaturated fat). After the conquest of Mexico by Spain, pork lard eventually became the main fat source used for preparation of tamales. Pork lard contains typically 38–43% saturated fats (mainly, palmitic acid) and 56–62% unsaturated fats (mainly, oleic acid), producing soggy tamales, with high cholesterol contents. In recent decades, vegetable fat (VF), specifically hydrogenated vegetal shortening has been increasingly used. In contrast to AF, the content of VF is dominated by saturated fats.[11] Differences in composition between AF and VF can lead to physicochemical transformations that may affect the digestibility and glycemic response of tamales, and ultimately impacting consumer health. For instance, Lau et al.[12] reported that the type of fat used for baked bread affected the formation of amylose-lipid complex, with coconut oil having the lowest digestibility and glycemic response. The aim of this work was to produce masa using AF and VF, and to evaluate the effect of steam cooking at boiling temperature on the textural, thermal, and digestibility properties of tamales.

2. Experimental Section 2.1. Materials Tamales were prepared using commercial nixtamalized corn flour (F) with no additives and a mean particle size of 0.13 mm (Maseca S.A. de C.V, Monterrey, Mexico). Baking powder (Rexal, Monterrey, State of Nuevo Leon, Mexico), salt (La Fina, Sales del Itsmo, S.A. de C.V., Coatzacoalcos, State of Veracruz, Mexico), animal fat (AF; Pork lard, J.C. Fortes, Mexico City, Mexico; saturated fat 35.9% w/w), and vegetable fat (VF; INCA hydrogenated vegetable shortening, ACH Foods Mexico, S. de R.L. de C.V., Mexico City, Mexico; saturated fat 52.7% w/w) were purchased from Walmart, Mexico City, Mexico. Cornhusk leaves were purchased at Mexico City’s fresh produce central market. Pancreatin, α-amylase, pepsin, bile extract, linoleic acid, ammonium thiocyanate, and haemoglobin were purchased from Sigma–Aldrich S.A. de C.V. (Toluca, State of Mexico, Mexico). Distilled water was used in all experiments.

2.2. Masa Preparation Tamales were prepared as described by Figueroa-Cardenas et al.[9] Briefly, the components of the basic recipe for masa were water (46.8% w/w), nixtamalized maize flour (36.0% w/w), either AF or VF (15.8% w/w), baking powder (0.7% w/w), and salt


(0.7% w/w). The same formulation without AF or VF was used as control. All ingredients were mixed and kneaded in a bowl during 15 min until achieving the necessary consistency so that a small ball of the masa floated in a beaker of water. In specific case of the control sample, the masa just was mixed and kneaded during 10 min. To avoid dehydration, the masa formulations were left to rest for 5 min in the bowl before the experiments. Masas were coded as MC (control masa, without fat added), MAF (masa made with animal fat), and MVF (masa made with vegetable fat).

2.3. Tamales Cooking Masa portions of 100 g were molded into tubular shape, wrapped in cornhusk, flattened and placed in a digital food steamer (PureMate PM 10107, Super Tech Health Ltd., Great Barr, Birmingham, England), and cooked for 90 min, at 92 C (Boiling point of water in Mexico City). The cooked tamales were cooled down to room temperature, before proceeding with the analyses. The tamales were coded as TC (control tamal, without added fat), TAF (tamal made with animal fat), and TVF (tamal made with vegetable fat).

2.4. Rheological Properties A Physica MCR 300 rheometer (Physica Meβtechnik GmbH, Stuttgart, Germany), using parallel-plate geometry (upper serrated plate with 50 mm diameter) was used to determine the rheological properties of the masa formulations. The rheometer was calibrated against a standard provided by the manufacturer. Masa sample (5.0 g) was placed in the measuring system, and left to rest for 5 min at 25 C for structure recovery. The upper plate was lowered until the thickness of sample was adjusted to 5 mm and the excess was trimmed off. The edges of samples were covered with oil to reduce water evaporation. Temperature maintenance was achieved with Physica TEK 150P temperature control system. Flow curves were obtained by varying the shear rate from 106 to 103 s1. Amplitude sweeps were carried out, with strain ranging from 0.01–100% at 1.0 rad s1. The rheological parameters were obtained from the equipment software (US200/32 V2.50) in all cases.

2.5. Texture Profile Analysis (TPA) Texture profile analysis (TPA) was performed at room temperature on cylinders, 1 cm in diameter and 1.5 cm in height, using a Brookfield CT3-4500 texturometer (Middleboro, MA, USA). Each sample was cut from the central part of the tamales formulations using a borer and a sharp knife. In all cases the samples were compressed by 50% with the spherical probe TA18 (diameter ¼ 12.7 mm), using two compression cycles, at a constant crosshead velocity of 2.0 mm s1. The following parameters were quantified and are defined as:[13] hardness (the absolute peak force on the first down stroke), adhesiveness (the negative force area for the first cycle, representing the work

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necessary to pull the compressing plunger away from the sample), springiness (the height that the sample recovers during the time that elapses between the end of the first cycle and the start of the second cycle), cohesiveness (the ratio of the positive area during the second compression to that during the first compression), resilience (the ratio between the areas under the compression and decompression curves), and chewiness (hardness cohesiveness springiness). Parameters values were obtained from the equipment software (TexturePro CT, Middleboro, MA, USA).

spectra were recorded on a Perkin Elmer spectrophotometer (Spectrum 100, Perkin Elmer, Waltham, MA, USA) equipped with a crystal diamond universal ATR sampling accessory. Each spectrum represented an average of four scans. All spectra were deconvoluted using techniques described by using Gaussian and Lorentzian functions. In this case, the assumed line shape was Lorentzian with a halfwidth of 15 cm1. The resolution enhancement factor was chosen as 1.5.

2.9. In Vitro Digestibility 2.6. Thermal Analysis

2.9.1. Starch

2.6.1. Thermogravimetric analysis (TGA)

Total starch (TS) was measured according to AACC method 76.13.[15] Briefly, 100 mg of samples were treated with 2 M KOH to disperse all starch fractions, which then were hydrolyzed by incubation with α-amylase and amyloglucosidase (AMG). Resistant starch (RS) was measured using the AACC method 32–40.[15] The samples were incubated with pancreatic α-amylase and AMG for 16 h to hydrolyze the non-RS. Then, the reaction was stopped by the addition of ethanol. Finally, the samples were centrifuged to precipitate the RS. The pellet was then treated with 2 M KOH and hydrolyzed by incubation with AMG. For these determinations, the total and resistant starch kit analysis from Megazyme International Ireland Ltd. (Bray Business Park, Bray, Co., Wicklow, Ireland) was used. Available starch was calculated as the difference between total starch and RS. In vitro digestion of the different tamales variations was performed using the methodology by Englyst et al.[16] Briefly, samples (200 mg) were incubated with pancreatin from porcine pancreas (300 U/mL, P1750, Sigma–Aldrich, St. Louis, MO, USA) and amyloglucosidase (95 U/mL, A7095, Sigma–Aldrich) enzymes. A temperature of 37 C and incubation time of 120 min were used for both enzyme treatments. Starch classification was based on the rate of hydrolysis, RDS (digested within 20 min) and SDS (digested between 20 and 120 min). Values were adjusted at the available starch content previously determined.

TGA of tamales was carried out using a TA Instruments 2950 thermal analyzer (New Castle, DE, USA). Samples were heated from 0 to 300 C by applying a heating rate of 5 C min1. In all cases, 40–60 mg of sample was used for analysis. The flow rate of carrier gas (nitrogen) was kept at 100 mL min1. A computer connected to the thermogravimetric analyzer automatically recorded the changes in weight, and then processed the data.

2.6.2. Differential Scanning Calorimetry (DSC) The thermal characteristics of the tamales were studied using DSC (TA Instruments, Q1000, New Castle, DE, USA) previously calibrated with indium. About 7.0 mg sample was weighted in aluminum pan and hermetically sealed. Samples were heated from 25 to 200 C at a heating constant rate of 5 C min1. An empty aluminum pan was used as reference. Temperatures (Toonset, Tp-peak, Te-end) and enthalpy of thermal transitions (ΔH, J g1) were calculated using the equipment software (Universal Analysis 2000, New Castle, DE, USA).

2.7. X-Ray Diffraction (XRD) To evaluate the crystallinity structure of starch granules as affected by AF or VF, X-ray diffractograms (XRD) of tamales formulations were obtained using a diffractometer (Siemens D5000, Bruker AXS GmbH, Karlsruhe, Germany) with Cu-Kα radiation (λ ¼ 1.543) and a secondary beam graphite monochromator. Diffractograms were taken between 5 and 40 (2θ) at a rate of 1 s1 (2θ) and with a step size of 0.03 (2θ). The diffractograms were obtained at 25 C using an accelerating voltage of 40 kV and a current of 30 mA. The data were analyzed using DIFFRACplus Evaluation (Eva), Version 10.0 to calculate the crystallinity values. Diffractograms were smoothed (SavitskyGolay, polynome ¼ 2, points ¼ 15) and baseline corrected by drawing a straight line at an angle of 7 .

2.8. ATR-FTIR Spectroscopy Samples were characterized by ATR-FTIR spectroscopy according to the methodology reported by van Soest et al.[14] FTIR


2.9.2. Protein In vitro digestion of tamal samples for estimation of protein digestibility was carried out following the methodology described by Gawlik-Dziki et al.[17] Briefly, simulated saliva solution was prepared by dissolving 2.38 g Na2HPO4, 0.19 g KH2PO4, and 8 g NaCl, 100 mg of mucin in 1 L of distilled water. The pH was adjusted to 6.75 and α-amylase (E.C. 3.2.1.1.) was added to obtain 200 U/mL of enzyme activity. For gastric digestion 300 U/mL of pepsin (pepsin A, EC 3.4.23.1) was prepared in 0.03 mol/L NaCl at pH ¼ 1.2. On the other hand, simulated intestinal juice was prepared by dissolving 0.05 g of pancreatin (activity equivalent 4 USP) and 0.3 g of bile extract in 35 mL 0.1 mol/L NaHCO3. The simulation of gastrointestinal digestion of tamales was carried out as follows. A 1.0 g of sample was homogenized in Erlenmeyer (250 mL) for 1 min to simulate mastication in the presence of 15 mL of simulated salivary fluid. Then, samples were shaken for 10 min at 37 C and pH was adjusted at 1.2 using 5 mol/L HCl. Subsequently, 15 mL of

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simulated gastric fluid was incorporated. The samples were shaken for 60 min at 37 C. After digestion with the gastric fluid, the pH of samples was adjusted to 6.0 with 0.1 mol/L of NaHCO3 and then 15 mL of a mixture of bile extract and pancreatin was added. The pH off the extracts was adjusted to 7.0 with 1.0 mol/L NaOH. Finally, 5.0 mL of 120 mmol/L NaCl and 5 mL of mmol/L KCl were added. The prepared samples were subjected to in vitro digestion for 120 min, at 37 C and in darkness. Afterwards, samples were centrifuged and supernatants were used for further analysis. The protein content of supernatant was determined with the method reported by Bradford,[18] which uses the principle of protein-dye binding, with bovine serum albumin used as standard. The in vitro digestibility of proteins was estimated on the basis of total soluble protein content and the content of protein determined after digestion.

2.10. Statistical Analyses Data were analyzed using one way analysis of variance (ANOVA) and a Tukey’s test for a statistical significance P 0.05, using the SPSS Statistics 19.0. All experiments were done in triplicate.

3. Results and Discussion 3.1. Rheological Properties The rheological response provides information regarding the malleability of masas during the spreading in the corn husk wraps. Figure 1a presents the apparent viscosity of masas as function of the shear rate. In all cases, the masas showed shear thinning behavior that facilitated the molding of masa into tubular shape before being wrapped with the corn husk. MC exhibited the highest viscosity values over the whole shear-rate range. Added fats reduced the viscosity since this ingredient acted as a lubricant between the particles of maize flour. The effect was more pronounced for AF than for VF since the latter ingredient has a more solid-like behavior than the former one. Figure 1b presents the behavior of the storage (G0 ) and loss (G00 ) moduli with respect to the strain. It is noted that the masa formulations did not exhibit a linear viscoelastic behavior in the range of strain values studied. This effect is commonly exhibited by materials containing a large fraction of particles (e.g., starch granules).[19] On the other hand, MC exhibited the lowest viscoelastic moduli for strains