SUMMARY. The functional properties of Caryodendron orinocense protein product were investigated and compared with those of soybean (Glycina maxima). The product protein content was 24.47 g/100g (Nx6.25). Solubility increased at both sides of the isoelectric point (pH 4.0) and with increased NaCl concentration up to 0.5M. Compared with soybean flour (50% protein), the protein product exhibited higher water and oil absorption, but lower emulsifying activity, emulsion stability, foaming capacity, and foam stability, the last one increase at higher pH. Emulsifying activity, foaming capacity, and foam stability were ionic strength dependent. C. orinocense protein product increased its emulsifying activity steadily from 0.05M to 0.75M NaCl, while it remained almost constant for soybean flour. Foaming capacity increased drastically at ph 10. The minimum time and concentration to form a gel was 20% in 4 min and 10% in 8 min for the Caryodendron protein product and soybean flour, respectively. The bulk density was 0,5056± 0,0041 g/mL.

Key words: Protein product, Caryodendron orinocense, functional properties.

RESUMEN. Propiedades funcionales de un producto proteico obtenido del Caryodendron orinocense (nuez de Barinas). Las propiedades funcionales de un producto proteico del Caryodendron orinocense se evaluaron y se compararon con las de soya (Glycina maxima). El contenido proteico del producto evaluado fue de 24.47 g/100g (Nx6.25). La solubilidad se incrementó a ambos lados del punto isoeléctrico (pH 4.0), aumentando además en presencia de NaCl, en concentraciones por encima de 0.25M. Comparado con la harina de soya (50% proteína), el producto proteico presentó una capacidad de absorción de agua y aceite mayor, pero menor actividad emulsificante, estabilidad de la emulsión, capacidad espumante y estabilidad de la espuma. La actividad emulsificante, capacidad de formación de espuma y estabilidad de la espuma, fueron dependientes de la fuerza iónica. El producto proteico del C. orinocense aumenta en forma continua su actividad emulsificante con concentraciones de NaCl, manteniéndose constante de 0.05M a 0.75M, mientras que permanece constante para la soya. La formación de espuma aumentó drásticamente a pH 10. El tiempo y la concentración mínima para la formación del gel fue de 20% en 4 min y 10% en 8 min para el producto proteico del Caryodendron y la harina de soya, respectivamente. El producto proteico presentó un densidad de 0,5056± 0,0041 g/mL.

Palabras clave: Producto proteico, Caryodendron orinocense, propiedades funcionales.

INTRODUCTION

Proteins are important in food processing and food product development not only because of their nutritional properties but also because they are responsible for many functional characteristics that influence consumer acceptance of food. On the basis of their functionality, the proteins find use in diverse systems such as fabricated and texturized food products. Although Caryodendron orinocense Karst. is a tree, which grows wild at the base of The Andes in countries like Peru, Ecuador, Colombia and Venezuela, its seeds or nuts represents a good source of oil and proteins (1,2), and a potential raw material useful for the food industry. For efficient utilization and consumer acceptance of a protein product, studies on the functional properties are important. The functional properties of the flour were previously studied. However, a new protein product with a higher protein content was prepared (3) and the evaluation of its functional properties is the objective of this work.

MATERIALS AND METHODS

Was prepared by extracting ground Caryodendron flour with 95⁰ ethanol at a flour to solvent ratio of 1:30 for 15 min with constant stirring at 35⁰C. The slurry was centrifuged at 3000 rpm, for 30 min. The supernatant was discarded and the residue extracted twice more, then vacuum dried and stored in vacuumed plastic bags at 4⁰C (3). Soya (Glycine max) flour was obtained from Nestlé of Venezuela.

Proximate analysis of the protein product was determined according to the standard methods of the AOAC (4), with the exception of fiber, which was assessed in a Fibertec model M, (Tecator, Hoganas, Sweden). Carbohydrates were calculated by difference. Results were expressed on a dry matter basis, and all analyses were run in triplicate.

Protein solubility

Protein solubility of a 1% (w/v) water suspension was determined over a pH range from 2 to 12, and over a NaCl concentration from 0.0 to 0.75M at pH 6.4, according to the method previously described, Padilla, et al., (1). The percentage of soluble nitrogen was calculated.

The method described by Okaka & Potter (5) was used with 25g of the prepared product.

Water and oil holding capacity

To 2 g of sample, 20 mL of water, or 12 mL of corn oil (Mazeite, Remavenca, Turmero, Venezuela), was added, stirred in a vortex and held at room temperature (~ 25⁰ C) for 1 h. The procedure of Okaka & Potter (5) was followed.

Gel formation

Minimum gelling concentration and time needed to form a gel at this concentration was performed following the method described previously (1).

Emulsifying activity and emulsion stability were determined by the turbidimetric method of Pierce & Kinsella (6) with slight modification described by Padilla et al., (1).

These properties were assessed by the Srinivas & Rao Narasinga (7) method, using a 3% (w/v) suspension. Both FC and FS were determined as a function of pH and NaCl concentration as described by Padilla et al., (1).

All data used were means of triplicate (n=3) determinations, and analysed by (Kruskal Wallis) no parametric ANOVA to determine statistical differences at p<0.05 (8).

Results are shown in Table 1. The total crude protein content of the product protein evaluated was 24.47 g/100g using a conversion factor of 6.25.

TABLE 1

Proximate composition (g/100g) of protein product and flour from C. orinocense (Barinas nuts) ¹

Protein solubility

In Figure 1 the minimum nitrogen solubility for both samples was at pH 4 the isoelectric point (pI). Both samples also showed an increased solubility at both sides of the pI. Padilla et al., (1) reported similar behavior for the C. orinocense flour (protein content 17.78 g/100g), the difference is that the solubility of C. orinocense flours reaches a plateau at pH 8; while the protein product increase with the pH. These results suggest how the product will perform when incorporated in a food product (9), and indicate that the solubility is influenced by the origin, processing conditions and pH, besides others parameters are corroborated these results.

FIGURE 1

pH effect on the solubility profile of Caryodendron protein product

Figure 2 shows how NaCl concentration affects the solubility of proteins, which increases with NaCl concentration up to 0.5M and decreases at 0.75M. Some salts are effective in increasing protein solubility ("salting in" effect) and at the same time are also effective in destabilizing native globular and fibrous structure and increasing the rate of denaturation of native structures. During "salting out", a process that decreases solubility, there is a reverse effect on the stability and rate of denaturation of native proteins (10). The protein product presents a steady increase in solubility, more pronounce for the protein product than the flour as was reported by Padilla et al., (1). It also has a better solubility than soybean flour, as NaCl concentration increases, this is also important in the development of food products.

FIGURE 2

Nacl concentration effect on the solubility profile of Caryodendron protein product

There is no statistical difference in bulk density between both samples (Table 2). The small difference in values might be due to the smaller particle size for soybean flour.

TABLE 2

Water and oil holding capacity (WHC, OHC), emulsifying activity (EA), emulsion stability (ES), and foam capacity (FC) of protein product and soybean flour from C. orinocense (Barinas nuts) ¹