Interactions in interesterified palm and palm kernel oils mixtures . I-Solid fat content and consistency

By Renato Grimaldi , Lireny Aparecida Guaraldo Gonçalves , Luiz Antonio Gioielli 2 and Ilka S. Simões 2 Laboratório de Óleos e Gorduras – Faculdade de Engenharia de Alimentos (FEA) – Universidade Estadual de Campinas (UNICAMP), Caixa Postal 6091, CEP 13081-970, Campinas , SP, Brazil. E-mail: grimaldi@fea.unicamp.br Faculdade de Ciências Farmacêuticas – Universidade de São Paulo (USP). E-mail: lagio@usp.br


INTRODUCTION
The chemical interesterification is an important tool to modify the compositions of fats and oils.The performance of final product of hydrogenated oils and fats is due the physical alterations in the fatty acids (trans isomers).The interesterification does not modify the profile of the starting raw material.The modifications in the melting and solidification properties of interesterified oils and fats are due to relative proportions of acylglyceride components after fatty acids re-arrangement (Erickson, 1995).
The interesterification is frequently confirmed through color monitoring, melting point and solid fat profile.The fastest techniques to control are the monitoring of brown color and melting point, but only when melting point alterations exists.The development of brown color is only a tool to verify the reaction, but the complete re-arrangement is dependent of many factors, like catalyst choice, reaction temperature, oil quality (Laning, 1985, Gioielli and Barufaldi, 1988, Erickson, 1995).
The solids profile is the main tool to the specification of fats used in margarine and fat products.The reading must be done at 4 temperatures at least, like 10, 20, 30 and 35 o C or like 20, 30, 35 and 40 o C (Young, 1985).
The crystals amount in oil mixtures, determined by solid fat content, is responsible for many characteristics of the products, that include general appearance, organoleptic properties, spread facilities and oil exudation (Lida and Ali, 1998).
The solid fat content between 4 o C and 10 o C determines the spread facilities of the product at refrigeration temperature.The solids content at up to 32% at 10 o C, is essential to guarantee good performance of spread at refrigeration temperature (Lida and Ali, 1998).
The solid fat content between 20 and 22 o C determines the product stability and its resistance against oil exudation.The ideal solid contents must be at least 10%.Between 35 and 37 o C it determines the softness and smell properties in the mouth (Lida and Ali, 1998).
The solid profile has a good relation with hardness characteristics of plastic fats and contributes with the structure of final product (Woerfel, 1995).
Shortenings with small solid variation in a wide temperature range are defined as plastic fats.This plasticity is desirable in many products, as margarines and chocolates and can be used under several temperatures where aeration and crystalline structure at high temperatures are important.The plasticity range is less important in products used under controlled conditions or in melting state, like in frying (Woerfel,1995).
In some systems that contain fats, it is desirable a high solid content to promote an adequate crystalline structure in foods with a high content of fats, like margarines and chocolate under room temperature and low solid content in high temperatures, to promote an easy melting in the mouth (Woerfel,1995).
By definition, texture is a hardness measure of a product in a specified temperature.The consistency variation in a temperature range is defined as plasticity (Erickson, 1995).Texture, measured as consistency or plasticity, is one of the most important characteristics of fat products and is primarily determined through physical properties of fats and oils (Lida and Ali, 1998).
In margarines, texture appears as a very important parameter, because these products should have good spread properties under refrigeration and do not settle oils when leaved under room temperatures (Deman et al., 1991).
Texture and spreadability depends on two main factors, that include a solid fat content and process conditions during the cooling and crystallization of emulsion (List et al., 1995).The yield value parameter was described by (Haighton, 1959), and is considered as an independent parameter.The yield value is used to compare the several hardness index, obtained by penetrometers and other reological instruments.
The yield values in commercial margarines that were produced with hydrogenated soybean oil or mixtures of liquid and hydrogenated oils showed values from 200 g.cm -1 for soft products until 2800 g.cm -1 for hard products (List et al., 1995).
The values that influence yield value and must be considered are: softness and cone format, structural hardness, penetration time and kinetic energy of the cone (Haighton, 1959).

Methods
Free

RESULTS AND DISCUSSION
The normal solid profile behavior after chemical interesterification reaction between palm and palm kernel mixtures showed a consistency increase to samples with a high palm oil content and a consistency decreased to palm kernel oil (Laning, 1985).Allen (1996) cited that normally the interesterification is accomplished with a mixture of two oils and for some products that require a high consistency they can absorb in their formulation hydrogenated oils.Chemical specifications of raw materials and solid fat content of PO/PKO mixtures before and after interesterification can be visualized at Tables I and II.
The composition that contain up to 60% of PKO showed a consistency increase.In other fractions, with 80 and 100% PKO, the solid profile was lower.The desirable product must contain an intermediate solid content in a wide temperature range.The interesterification modify some melting properties and influence the velocity and morphology of crystals formation (Laning, 1985).
Palm kernel oil interesterified with small proportions of palm oil can be used in the preparation of coatings with good texture, without fragility at room temperature and with good melting properties (Goh, 1994).
Figures 2 and 3 show isosolid diagrams of palm and palm kernel oils compositions before and after interesterification. (Lefebvre, 1983) cited that isosolids curves can be used to prove an eutectic system in oil mixtures.These diagrams represent under constant temperature, the solid content of several PO/PKO compositions (Rousseau et al., 1996).
The behavior alteration in an isosolid profiles before and after interesterification characterizes the eutectic system formation.(Balbo and Gioielli, 1991) demonstrate that an efficient way to visualize an eutectic system is the depression curve, that was minimized after interesterification. (Young, 1985) cited that this softness effect can be useful in some cases, like in margarines obtained with palm and palm kernel oils mixtures.By the other side, the incompatibility between cocoa butter and substitutes promotes structure crystalline modification and softness of chocolate during the storage (Lannes and Gioielli, 1995).
The texture values, represented by yield value showed similar behavior that solid profiles.The consistency improve was noted at 40/60 fraction after interesterification and at 25 o C a high consistency improvement was detected, that contributes to a better plasticity.eutectic effect was proved through yield values.This effect can be best visualized by consistency decreased at 20 o C of the samples before interesterification at 80/20, 60/40 and 50/50 fractions.The Table III shows the yield values obtained for PO/PKO fractions.
The isoconsistency curve (Figures 4 and 5) is another way to visualize this effect.
The linearity absence at the evaluated range is cited as an important aspect to identify eutectic system.To the mixture of two components, (Hare, 1974) describes a mathematical model based on quadratic answer to solid fat index (SFI) values and that the factors are dependent, contrary to factorial experimental, where one of the factors can be varied independently.
The increase of linearity, observed at 80/20 and 60/40 fractions, after interesterification is an evidence that the technological process decreased the incompatibility and that this mixtures can reach more industrial applications than the original ones.
Figure 2 Isosolid curves of binary mixtures of PO/PKO before interesterification.
Figure 4 Isoconsistency curves of binary mixtures of PO/PKO before interesterification.

Table III Yield value (g.cm -1 ) of PO/PKO mixtures before and after interesterification.
Mean of standard deviations observed at each temperature -± 6% (yield value content).