2018 Volume 24 Issue 3 Pages 519-530
This work investigated the effects of okra (Abelmoschus esculentus) gum addition, as a fat replacer in ice cream. Water-extracted okra gum was used to replace the fat in ice cream at 0, 22, 44, 55, 88 and 100% to produce Super Premium (18% fat), Premium (14% fat), Regular (10% fat), Economy (8% fat), Low-fat (2% fat) and Zero-fat (0% fat) ice cream. The addition of okra gum was found to be comparable with full fat ice cream in term of melting rate and texture analysis. Droplet size data for the Super Premium ice cream displayed a bimodal distribution, whilst Zero-fat ice cream exhibited a monomodal droplet distribution. Rheological test, demonstrated that, Economy ice cream was the most elastic (G′). The substitution of fat content in ice cream with okra gum increased the viscous modulus (G″). Sensory results indicated that, up to 55% replacement of fat with okra gum was feasible to achieve satisfactory ice cream properties.
Okra (Abelmoschus esculentus (L.) Moench) is a flowering plant that produces edible green pods (Noorlaila et al., 2015; Sengkhamparn et al., 2010; Sengkhamparn et al., 2009a). Okra pods, when cooked produce a viscous and slimy mucilage, also called okra gum, which is a polysaccharide-rich hydrocolloid (Ndjouenkeu et al., 1996). The okra polysaccharides contain acidic polysaccharides comprising of glucose, galactose, rhamnose, galacturonic acid and glucuronic acid (Lengsfeld et al., 2004; Whistler and Conrad, 1954). There have been a number of studies on the extraction, rheological and physicochemical properties of okra polysaccharides (Samavati, 2013; Sengkhamparn et al., 2010; Sengkhamparn et al., 2009a; 2009b), as well as research that has attempted to use okra gum as a fat substitute, which has been investigated in cookies and frozen dairy desserts, whereby these studies evaluated the consumer's acceptance (sensory evaluation rating) and determined that, okra gum was a satisfactory fat replacer in their tested products (Romanchik-Cerpovicz et al., 2002; 2006).
Fat replacers, usually protein- or carbohydrate-based, are substances added to fat reduced food, in order to provide a fat-like organoleptic or physical properties (Akoh, 1998; Daniel, 2010; Karaca et al., 2009). In the food industry, commercially available plant and microbial gums such as carrageenan, guar gum, alginate, maltodextrins, pectin, galactomannans and xanthan gum are widely used as stabilizers, however, they have also shown to be effective carbohydrate-based fat replacers in low-fat products. This is attributable to the water binding characteristics of polysaccharide gums that can consequently restrict the mobility of water in food products, which can imitate the fatty mouthfeel (Akoh, 1998; Daniel, 2010). The water manipulating characteristics is achieved by the dynamic hydrocolloids random coil polymer, and is desirable since low fat food products have higher amounts of water than their high-fat counterparts. The type of hydrocolloid will determine the flexibility and space occupancy of the polymer networks, thus influencing the properties of the end food products in terms of viscosity, texture and rheological behavior (Clegg, 1996).
High fat food intake has often been associated with a number of degenerative diseases, such as heart diseases, diabetes, obesity and cancers. This has led health-conscious consumers to improve their dietary habits by reducing their fat intake, and choosing low-fat food alternatives. However, fats and oils in food are crucial components affecting dynamic sensory perception and textural changes during oral processing of the food (van Aken et al., 2011; Liu et al., 2015), therefore, extensive research and development has been carried out, in discovering and utilizing fat substitutes or replacers in food products (da Silva et al., 2016, Gupta et al., 2015; Javidi et al., 2016; Jiménez-Colmenero et al., 2010, 2012; Tanti et al., 2016). One of the most notoriously desserts, which is usually associated with having a very high fat content, is ice cream. Ice cream and frozen desserts are one of the many products that have garnered a lot of research interest in the use of carbohydrate-based fat replacers. Ice cream possesses an intricate colloidal mix of foam and emulsion, consist of fat globules, ice crystals and air bubbles (Goff, 1997). Typically, standard ice cream contains 10–16% of fat (Clarke, 2012; Goff and Hartel, 2013), which contributes to more than just flavor, it improves creaminess and mouthfeel, and is also essential for the texture, viscosity, ice crystallization, melt resistance and foam stability (El-Nagar et al., 2002; Karaca et al., 2009; Ohmes et al., 1998). The exclusive desired destabilization of fat in ice cream, is crucial to the final creaminess and stability of the aerated ice cream mix (Adapa et al., 2000). Aime et al. (2001), studied the effects of a modified starch on fat reduced ice cream, and observed that a decrease in fat even as low as 5%, was still able to produce similar textural and sensory qualities as regular (10% fat) ice cream. Other studies have also explored the preparation of ice cream with various types of carbohydrate-based fat replacers (El-Nagar et al., 2002; Karaca et al., 2009). Okra gum was chosen as the carbohydrate based fat replacer in this work due to okra's cheap price and easily available all year round. Previous work on the use if okra gum as fat substitute investigated in frozen desserts focused more on the sensorial acceptance only (Romanchik-Cerpovicz et al., 2006), whereas the main objective of this study, is to investigate the effects of okra gum as a fat replacer in ice cream, in terms of the physicochemical and sensorial characteristic of the produced ice cream.
Materials Tender okra pods grown in Malaysia were obtained from a local market. The ice cream ingredients included, UHT cream containing 35.5% fat (Anchor, Auckland, New Zealand), skim milk powder (SunLac, product of New Zealand but packed locally in Malaysia), sucrose (standard granulated sugar, MSM Prai Berhad, Malaysia), vanilla essence (Star Brand, Malaysia) and monoglycerides emulsifiers used for demulsification in preparation of ice cream mix (distilled, Ekömul MG 95 HP, Futura Ingredients, Malaysia).
Methods
Okra gum extraction Aqueous okra gum extraction was done according to the methods described by Romanchik-Cerpovicz et al. (2006, 2002) with slight modifications, in terms of the water ratio used. Initially, the okra pods were cut and the seeds were removed. Subsequently, the pods were heated at 80°C for 1 hour in water, with an okra to water ratio of 1: 3 (w/w). The mixture was then cooled to room temperature and filtered with a muslin cloth to remove the okra pods. The aqueous solution of okra gum was used in the ice cream formulation. The okra gum obtained was immediately subjected to a viscosity test after extraction, to ensure uniformity before using it in the ice cream formulation.
Viscosity test The apparent viscosity of the aqueous solution of okra gum obtained after the extraction procedure, was immediately examined using a Brookfield viscometer (USA) with a spindle diameter of 21 mm and a speed of 20 rpm at 25°C.
Proximate composition Proximate composition was carried out on the aqueous okra gum using the AOAC official methods (AOAC, 2006) to determine the moisture, fat, crude protein and ash content. Total carbohydrate content was obtained by difference: 100% − (crude protein% + ash% + crude fat % + moisture%).
Ice cream processing Ice cream of six different variations in their fat and okra gum percentage were formulated in this study, as shown in Table 1. The base ice cream mix consisted of 15% (w/w) skim milk powder, 15% (w/w) sucrose and 0.5% monoglycerides (Cottrell et al., 1979). The source of fat in this study, was from the UHT cream. The skimmed milk powder was initially dissolved in water and cream, and heated to 50°C with continuous slow stirring. The aqueous okra gum was added to the mixture at this stage. Premixed dry ingredients were subsequently added to the mixture and homogenized (Ultra Turax, IKA T25 equipped with standard dispersing elements S25N-25G, Germany) for 3 min before being pasteurized at 70°C for 25 seconds, using the double boiling method. The mixture was then homogenized using a high-pressure homogenizer (Panda, No 2805, Italy) and cooled to room temperature. Monoglycerides were added to the mixture, prior to placing the ice cream mix at 4°C overnight, for the aging process. The vanilla flavor was then added, and the mixture was beaten using an electric mixer (Pensonic, PM112, Malaysia) for 5 min, then stored at −18°C for 1 hour. The mixture was then beaten again for 5 min and placed at −18°C again for 2 hours, followed by a final beating of 1 min. The semi-frozen ice cream was allowed to harden at −18°C for at least 24 hours.
| Ice cream | Ingredient % (w/w) | ||||||
|---|---|---|---|---|---|---|---|
| UHT cream | Okra gum | Sucrose | Skim milk powder | Vanilla essence | Mono-glyceride | Water | |
| Super premium | 50.7 | 0 | 15.0 | 15.0 | 0.5 | 0.5 | 18.3 |
| Premium | 39.4 | 4.0 | 15.0 | 15.0 | 0.5 | 0.5 | 25.6 |
| Regular | 28.2 | 8.0 | 15.0 | 15.0 | 0.5 | 0.5 | 32.8 |
| Economy | 22.5 | 10.0 | 15.0 | 15.0 | 0.5 | 0.5 | 36.5 |
| Low-fat | 5.6 | 16.0 | 15.0 | 15.0 | 0.5 | 0.5 | 47.4 |
| Zero-fat | 0 | 18.0 | 15.0 | 15.0 | 0.5 | 0.5 | 51.0 |
Melting resistance test The melting resistance test was performed based on Clarke's (2012) protocol. Hardened ice cream (5 × 5 × 2.5 cm) was positioned on a wire mesh (opening size 5 mm × 5 mm) in a closed room at 25°C and allowed to melt. The weight of the melted ice cream was recorded at every 1 min interval, up to a maximum of 120 min or until the ice cream had completely melted. Each measurement was carried out in at least three replications.
Texture analysis The ice cream texture test was performed based on the protocol described by Aime et al. (2001), with slight modifications. Hardness and tackiness profile of the ice cream samples were analyzed using the Texture Analyzer Twin-Column (Shimadzu AGS-J 500N, Kyoto, Japan). Texture analysis was carried out using an acrylic cylindrical probe (2.5 cm in diameter, 3.5 cm length), with a penetration depth of 15 mm and 5.0 kg force. Hardness was measured by the positive peak force from the probe penetration, while the tackiness of ice cream was measured by the negative peak force achieved during the probe withdrawal. Each measurement was carried out in at least three replications.
Droplet size determination The droplet size distribution measurement was carried out similar to Sofian-Seng et al. (2017), using a laser diffraction technique (Malvern Mastersizer 2000, Malvern Instruments Ltd., UK). The absorbance value of the emulsion particles was 0.001. Refractive Index of 1.462 was used for considering the milk-fat refractive index as a reference. The ice cream samples were diluted with water (1:10) before being pipetted into the water in the measuring cell unit (Hydro MU). Measurements were carried out when the instrument displayed an obscuration rate of 11–12%.
Rheological analysis The rheological test performed, was carried out according to the method reported by Sun-Waterhouse et al. (2013). Each hardened ice cream sample was taken out of the freezer prior to every measurement. A cube (1 × 1 × 1 cm) of ice cream was loaded onto the rheometer (Physica MCR301, Anton Paar GmbH, Graz, Austria) with a cone-and-plate geometry (47 µm gap, 50 mm diameter, 2° angle). The ice cream was allowed to equilibrate with the Peltier plate system for 2 min at −5°C. The linear viscoelastic region was determined by running the amplitude sweep test at constant frequency of 10 s-1 and a strain range from 0.001 to 100%. The frequency sweep test was then conducted between 0.1 and 1000 Hz. Data obtained was analyzed using the Rheoplus software (Anton Paar GmBH, Graz, Austria), and the dynamic elastic or storage modulus (G′) as well as the dynamic viscous or loss modulus (G″) were observed.
Sensory evaluation The hedonic test method is typically conducted, to evaluate the sensory and acceptance levels of consumers to the different ice cream formulations. A total of 34 untrained panelists and a 7-point hedonic test were used. Each panelist was served six different samples of ice cream (50 g each), with a three digit random number coding. Attributes evaluated were color, aroma, creaminess, texture, sweetness, after taste and overall acceptance.
Statistical analysis All physical analyses were carried out at least in triplicate, and the data was reported as a mean of each analysis. Pearson's correlation coefficients was used to demonstrate the correlation between variables and percentage of fat replacement using Minitab 17. Results were considered significant for p < 0.05. Principal component analysis (PCA) was conducted and plotted by using The Unscrambler × 10.2. Curves and bar graphs were constructed using SigmaPlot 12.0.
Viscosity and composition of extracted okra gum The viscosity of the extracted okra gum using okra to water ratio of 3:1 (w/w), with 20 rpm circulation, was 2.06 ± 0.12 Pa.s. The viscosity of every okra extract was adjusted with water, to achieve a reading within the same range, to be used for every batch of ice cream produced in this study. Proximate analysis on the extracted okra gum obtained showed it contained 66.15% moisture, 31.49% carbohydrate, 2.13% protein, 0.12% crude fat, and 0.11% ash.
Melting resistance and overrun of ice cream The melting resistance of ice cream tested in this study is shown in Figure 1. The Super Premium ice cream had the slowest melting rate and took 126 minutes to melt completely. This was followed by Premium, Economy, Low-fat, Regular and Zero-fat ice cream. The efficiency of thermal diffusion can be reduced by increasing the fat content, due to the lower thermal conductivity of fat compared to water (Akbari et al., 2016; Soukoulis et al., 2008). This is evident in that, the ice cream trends showed an improvement in melting resistance with increasing fat content. High Pearson correlation coefficient (0.826) was observed between the half-life period of melting-down (MD-50) and fat replacement percentage (p = 0.000) as shown in Table 2. This is because amount of fat in ice cream formulations contributes significantly to the end structure of ice cream, as the fat globules undergo partial coalescence during freezing and whipping of the mix, which has been reported to provide the three-dimensional frame that holds the air bubbles, ice crystals, fat globules and unfrozen serum together (Akbari et al., 2016; Allen et al., 2006; Goff, 2008; Koxholt et al., 2001). Méndez-Velasco and Goff (2012) reported a decrease in ice cream stability, when the fat percentage was reduced in the formulation. Similar findings were reported by Karaca et al. (2009), even with the use of fat replacers. El-Nagar et al. (2002) reported that, ice cream with reduced fat and fat replacers melt faster, which consequently decreases the consumer acceptance of creaminess. Although hydrocolloids are used in ice cream as stabilizers, and improves resistance to melting (Regand and Goff, 2003), the substitution of fat with 100% okra gum, recorded the fastest melting rate in Zero-fat ice cream. However, the melting rate of Zero-fat ice cream was observed to be very similar to that of three other ice cream samples namely, the Low-fat, Economy and Regular. Figure 2 shows the overrun of ice creams, which exhibit reduction of air incorporated into the ice cream as the fat content decreases. The absence of fat in Zero-fat ice cream resulted in nonexistence of overrun (1.88 ± 0.36%), whereas Super premium ice cream resulted in the highest overrun (74.77 ± 4.52 Negative Pearson correlation coefficient (−0.983) was observed between the overrun and fat replacement percentage (p = 0.000). The amount of air incorporated also influenced the rate of melt-down (Muse and Hartel, 2004). The regression coefficient (−0.463) showed that mean MD-50 decrease with the increase of overrun (p = 0.000). Although, in some case polysaccharide added into oil-in-water (O/W) emulsion can form complex with the protein emulsifiers, the competitive adsorption is very much dependent on the charge of the protein-coated droplets as well as the polysaccharides (Cho et al., 2009). The okra gum in this study also increases the viscosity of the ice cream mix. Adapa et al. (2000) reported that, an increase in viscosities as a result of the addition of carbohydrate stabilizers, helps to stabilize the cream foam, but does not have much effect on the foaming capacity (Stanley et al., 1996), which demonstrated the ability of plant polysaccharides such as okra gum to maintain the air bubbles inside the ice cream structure, but not the incorporation of it. Furthermore, it has been reported that slower melt down was achievable with higher level of partially coalesced fat globules (Zhang and Goff, 2005).
Meltdown percentage of ice cream at 25°C (n = 3)
| Variable | % of fat replacement | Overrun | ||
|---|---|---|---|---|
| Pearson correlation coefficient, r | p-value | Pearson correlation coefficient, r | p-value | |
| MD-50 | 0.826 | 0.000* | −0.756 | 0.000* |
| Overrun | −0.983 | 0.000* | ||
MD-50, half-time of melting down.
Overrun (%) of ice cream samples. Values represent means (n = 3) ± SD.
Texture analysis of ice cream The hardness and tackiness of ice cream samples is shown in Figure 3. The results demonstrated no apparent effect of fat replacement with okra gum on the hardness of ice cream. Zero-fat ice cream was found to be the hardest, with a recorded force of 22.9 ± 0.1 N and interestingly, had no significant difference (p > 0.05) with Premium and Regular ice cream which contained 14 and 10% fat, respectively. The Super premium sample was the least hard at, 4.8 ± 0.8 N and was not statistically different (p > 0.05) from the Economy ice cream. This is in agreement with the findings reported by Guinard et al. (1996) and El-Nagar et al. (2002) that a higher fat content in ice cream is inversely proportional to hardness. Hardness and tackiness both showed negative Pearson correlation coefficient of −0.615 (p = 0.033) and −0.887 (p = 0.000) with fat replacement respectively, as shown in Table 3. The addition of food gum influenced the ice cream texture, due to water absorption by the polysaccharides, increasing the viscosity of the aqueous phase and, consequently decreasing the ice crystal growth (Akbari et al., 2016; Jimenez-Flores et al., 1993; McGhee et al., 2015; Schmidt et al., 1993). However, though the Low-fat and Zero-fat ice cream samples contained a higher percentage of okra gum, the stabilizing effect due to an increase in viscosity, diminished. This could be accredited to the fact that these ice cream samples also contained a higher percentage of water, thus increasing the ice phase volumes. Karaca et al. (2009) in their study described, the possibility that the milk fat interacts with various fat replacers, which in turn influences the structure and melting properties of the ice cream. This might be the case for Economy ice cream, which exhibited a lower hardness level, and was not significantly different (p < 0.05) from Super Premium ice cream. Results from the tackiness data, revealed two distinct populations of ice cream; the least adhesive were the Economy, Low-fat and Zero-fat group, while the Super premium, Premium and Regular ice creams recorded higher tackiness. The hardness and tackiness of ice cream is determined by the internal structure of the ice cream, hence a reduction in the amount of fat will increase the ice crystals, making the ice cream less sticky. However, this is contrary to what El-Nagar et al. (2002) reported in their study, they observed that, there was lower tackiness in high fat yogurt ice cream as compared to low fat ice cream.
Hardness (positive peak force (N)) and tackiness (negative peak force (N)) of ice cream samples as measured using Texture Analyzer. Values represent means (n = 3) ± SD.
| Dependent variable | % of fat replacement | |
|---|---|---|
| Pearson correlation coefficient, r | p-Value | |
| Hardness | −0.615 | 0.033 * |
| Tackiness | −0.887 | 0.000* |
| d4,3 | 0.771 | 0.000* |
d4,3, volume weighted mean diameter.
Droplet Size Distribution of Ice Cream The droplet size distribution of ice creams produced, is depicted in Figure 4. The Super premium ice cream displayed a bimodal distribution with the largest droplet size. This was followed by Premium and Regular ice cream. The bimodal distribution peak for Economy and Low-fat ice cream was shifted to a smaller droplet size range. Only Zero-fat ice cream produced monomodal peak distribution. The smallest and narrowest droplet distribution peak exhibited by the Zero-fat ice cream, was due to the omitted fat in its formulation and the lack of partial coalescence of fat globules. It was also observed that, a decrease in fat concentrations resulted in a decrease in the mean droplet size. The highest volume weighted mean diameter (d4,3) was obtained with Super premium sample (d4,3 = 51.46 ± 5.01 µm), followed by Premium (d4,3 = 13.86 ± 1.28 µm), Regular (d4,3 = 4.49 ± 0.16 µm), Economy (d4,3 = 0.47 ± 0.00 µm), Low-fat (d4,3 = 0.27 ± 0.00 µm) and Zero-fat (d4,3 = 3.466 ± 0.75 µm) ice cream. Furthermore, d4,3 showed significant correlation with percentage of fat replacement with Pearson correlation coefficient of 0.771 (p = 0.000). d4,3 has been reported to be more sensitive to fat aggregation compared to the Sauter mean diameter (d3,2) (Relkin and Sourdet, 2005). This was apparent with the higher fat content ice cream in this study which also had larger secondary droplet distribution peak. The two peak droplet distribution in ice cream, has been reported by various researchers (Bolliger et al., 2000; Bolliger et al., 2000; Goff, 2008; Goff and Hartel, 2013; Granger et al., 2005; Sofian-Seng et al., 2017), where the second smaller peak was a result of partially coalesced fat globules produced during whipping of the ice cream mix in the presence of second emulsifier (Gelin et al., 1996; Goff, 1997). In this study, monoglycerides were added to induce the partial coalescence desired in ice creams, which has been reported to give ice cream its texture and creaminess (Benjamins et al., 2009; Zhang and Goff, 2005).
Droplet size distribution of Super premium (d4,3 = 51.46 ± 5.01 µm), Premium (d4,3 = 13.86 ± 1.28 µm), Regular (d4,3 = 4.49 ± 0.16 µm), Economy (d4,3 = 0.47 ± 0.00 µm), Low-fat (d4,3 = 0.27 ± 0.00 µm) and Zero-fat (d4,3 = 3.466 ± 0.75 µm) ice cream. Values represent means (n = 3) ± SD. d4,3, volume weighted mean diameter.
Rheological measurement of ice cream The storage modulus (G′) and loss modulus (G″) were obtained for all the ice cream treatments, to investigate the rheological properties in terms of the viscous and elastic properties (Figure 5). All ice cream samples tested, showed dependency towards the frequency, a common trait of typical viscoelastic material. The G″ obtained was also higher than G′ across all samples. Adapa et al. (2000) reported a reduction in the elastic properties, G′ due to a decrease in fat content in their ice cream while using fat replacers. However, the same trend was not observed in this study. Interestingly, Economy ice cream was found to be the most elastic followed by Premium, Super Premium and Regular ice cream. Low-fat and Zero-fat ice cream exhibited very low levels of elastic properties as compared to the others. The viscous properties G″ of the ice creams, could be divided into two distinct groups, a higher G″ obtained with Super Premium, Regular, Premium and Economy ice cream and a much lower G″ obtained with Low-fat and Zero-fat ice cream. The results of this study corroborated with those of Adapa et al. (2000), whereby, the substitution of fat content in ice cream with carbohydrate-based fat replacers did not enhance the elastic properties but instead increased the viscous properties of the ice cream. This was expected due to the ability of carbohydrates to imbibe high amounts of water (Akoh, 1998; Jimenez-Flores et al., 1993; McGhee et al., 2015; Schmidt et al., 1993). Water-extracted okra polysaccharides have been reported to be acidic polysaccharides, predominantly made up of galactose, rhamnose, galacturonic acid (Whistler and Conrad, 1954), glucose and glucuronic acid (Lengsfeld et al., 2004). Okra gum in solution has been reported to exhibit viscoelastic behavior (BeMiller and Whistler, 2012).
Storage modulus G′ and elastic modulus G″ of Super premium, Premium, Regular, Economy, Low-fat and Zero-fat ice cream as a function of frequency. Values represent means (n = 3) ± SD.
The tan δ values in Figure 6 exhibited that fat content affect the viscoelastic properties of ice cream. Super premium, Premium and Economy ice cream had lower tan δ curves compared to Low-fat and Zero-fat ice cream. Adapa et al. (2000) had similar findings, in which their ice cream with 12% milk fat had significantly lower tan δ values than ice creams containing fat replacers. However, there are no apparent linear trend of G′, G″ and tan δ due to the reduction of fat content or the increase of okra gum in the ice cream. This could be due to the synergistic effect of fat and okra gum. Replacement of fat content up to 55% (Economy ice cream), still exhibits similar characteristic to high fat (18%) ice cream. The degree of fat destabilization particularly partial coalescence has been reported to influence the elastic properties G′ (Adapa et al. 2000). The decrease in fat destabilization as fat content decreases, has previously been demonstrated by the lacking of second smaller peak on the droplet distribution profile (Figure 4), and may be correlated to the reduction of the elastic properties G′ in the ice creams observed in this study. The second smaller peak has been described as partially coalesced fat globules (Gelin et al., 1996; Goff, 1997).
Tan δ of Super premium, Premium, Regular, Economy, Low-fat and Zero-fat ice cream as a function of frequency. Values represent means (n = 3) ± SD.
Sensory evaluation of ice cream The Premium ice cream was found to be the most acceptable in terms of color attributes, with a mean score of 5.79 ± 0.84 (Figure 7). However, no significant differences (p > 0.05) were observed for the color attributes of Super Premium, Premium and Regular ice cream. The aroma of Super Premium ice cream was most preferred with a mean score of 5.29 ± 1.16, followed by the Premium > Regular> Economy> Low-fat > Zero-fat ice creams. The reduction of fat content to 2% and 0%, in Low-fat and Zero-fat ice cream respectively, significantly (p < 0.05) lowered the aroma scores. Fats in ice cream also function as carriers of volatile aromatic components, hence a reduction in fat content will influence the direct perception of flavors (Jones, 1996).
Score distributions of sensorial attribute of Super premium, Premium, Regular, Economy, Low-fat and Zero-fat ice cream ice creams: colour, aroma, creaminess, texture, sweetness, aftertaste and overall acceptance by 34 untrained panelist.
Super premium ice cream also recorded the highest creaminess mean score of 5.18 ± 1.66, followed by the Premium > Regular > Economy > Low-fat > Zero-fat ice creams. A decrease of fat content from 18% to 8%, showed no significant differences (p > 0.05) in terms of creaminess. The texture, mouthfeel and creaminess of ice cream is contributed by the milk fat (Akoh, 1998; Giese, 1996). However, in this study, milk fat substitution by okra gum, managed to provide or mimic the fat creaminess to a certain extent. Okra gum contains pectin (Sengkhamparn et al., 2010), and these pectin components can build a cross-linked gel in water in the presence of calcium ions (Cho et al., 1999). It has been established that, these gel cross-linked networks or polysaccharide entanglements, mimic the physical and sensory characteristics of emulsified fats (Sala et al., 2007). In terms of the texture attribute, the Premium ice cream had the highest mean score of 4.59 ± 1.87, followed by the Super premium > Regular > Economy > Low-fat > Zero-fat ice creams. Based on the findings of the texture scores, the ice creams could be separated into three distinct populations; the Super premium and Premium, Regular and Economy, and lastly Low-fat and Zero-fat ice creams, with significant difference (p < 0.05) recorded between all three.
No significant differences (p > 0.05) were observed for the sweetness attributes, of the Super Premium, Premium, Regular and Economy ice cream. The function of sucrose in the mixture is to lower the freezing point, sweeten the ice cream, increase viscosity and improve flavor and texture of the ice cream (Schmidt, 2008). Although the percentage of sucrose in the formulation was the same, panel scores on the ice cream sweetness varied. Sweetness sensation as well as flavor release, are very much influenced by the presence of fat (Soukoulis et al., 2010). The aftertaste attribute scores determined whether the okra gum addition caused an undesirable aftertaste to the panelists. Premium ice cream recorded the highest mean score of 4.97 ± 1.67, and significantly (p < 0.05) lower scores were recorded for Low-fat and Zero-fat ice creams. This was indicative that, okra gum might have adverse effects on aftertaste at high percentages. The overall acceptance mean score of Premium ice cream, with a 22% fat substitution was the highest at 5.03 ± 1.56. It was also determined that, fat substitution up to 55% in Economy ice cream had no significant difference (p < 0.05) on overall acceptance than with Premium ice cream. However, the Super premium ice cream investigated in this study did not obtain the highest acceptance score, as predicted because of some lactose crystallization because of the presence of excessive fat content in the ice cream composition.
Principal component analysis To compare all the sensorial and physical data, PCA analysis was carried out, which explained 64% of the data variation by the first component (Factor 1) and 14% variance by the second component (Factor 2) as shown in Figure 8. Variation in the ice cream formulations were apparent as it move from negative to positive values of Factor one, corresponding from the lowest fat content ice cream to the highest. Hardness, tackiness and MD-50 values had high loading with Zero-fat and Low-fat ice cream, demonstrating the lack of fat in the ice creams had effect to these attributes. Overall acceptability is close to sweetness, texture and creaminess. These attributes were associated with Regular and Economy ice cream. Whereas, overrun, fat content and d4,3 were closer to Super Premium ice cream.
Principal component analysis biplot based on sensorial and physical analyses of Super premium, Premium, Regular, Economy, Low-fat and Zero-fat ice cream ice creams
The findings of this study demonstrated that, okra gum has potential as a fat replacer in ice cream. Satisfactory melting resistance, texture and rheological properties were observed up to 44–55% of fat substitution, with Regular and Economy ice cream. The overall acceptance based on the sensory analysis for the Economy ice cream, was not significantly different with that of high-fat ice cream. It was observed that, complete substitution (100%) of fat with okra gum was not acceptable, which was expected due to the lack of structural networks of fat globules. Since fat contributes to various different functions in ice cream, a single fat replacer may not be sufficient to stimulate the structural and sensorial properties of fat, thus it is suggested that okra gum be used in combination with other types of fat replacers, to enhance the fat replacer properties.
Acknowledgements The authors would like to acknowledge the School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, which provided all the facilities necessary for this research.
