A novel process to improve the characteristics of low‐fat ice cream using date fiber powder

Abstract The objective of this study was to improve the characteristics of low‐fat ice cream (LFIC) using date fiber powder (DFP). DFP was added to LFIC mix (3% fat, 14% milk solids nonfat, 15% sucrose, 0.3% stabilizer, and 0.1% vanilla) at a rate of 1.5%, 2.5%, and 3.5%. Control treatment with no DFP was also manufactured for comparison. The LFIC mix was analyzed for physicochemical and microbiological analyses. After manufacture, microbiological, rheological, and sensory characteristics of LFIC were evaluated during storage at −18˚C for 30 days. The addition of DFP to the LFIC mix led to increasing (p < .05) the density and weight per gallon (lb) of final product. Thus, a 3.5% of DFP led to increasing the density of LFIC from 0.6 to 1.0 g/cm3 and weight per gallon from 5.2 to 9.0 lb, while the overrun of LFIC was decreased (p < .05) from 50.0% to 24.0%. Additionally, the melting resistance of LFIC made with DFP was higher (p < .05) as compared to control. Approximately 60% of LFIC made with DFP was melted after 50 min compared to 100% in control. The total bacterial count (TBC) and yeast and molds' count slightly increased in LFIC with adding DFP. However, there was a slight decrease in these counts during storage for 30 days. Psychrotrophic and coliform bacteria were not detected in the LFIC. Organoleptically, LFIC made with DFP showed higher scores (p < .05) of body and texture, melting quality, and appearance as compared to control during the 30 days of storage. However, the flavor was slightly decreased (p < .05) as the concentration of DFP was increased. The overall scores were increased with increasing the DFP concentrations up to 15 days as compared to control, followed by a decrease at 30 days of storage.


| Preparation of DFP
The pulp of Siwi date (local market, Asyut, Egypt) was extracted from the kernel by boiling in water for 15 min to make the sugars (sucrose, glucose, and fructose) soluble. Afterward, date fibers and pits were recovered through filtration using a 0.2-mm sieve. The pits were then removed, and the fibers were concentrated by rinsing in 40˚C water. Filtration was performed until the residue was free of sugar, which took approximately five successive rinsings. The residues were then pressed, dried in the oven at 65˚C for 24 hr, and milled in a blender at 5000 rpm to get Siwi date fiber powder (DFP) with <0.2 mm particle size. The concentrate was stored at −18˚C until further analyses (Yangılar, 2015). Siwi date and final DFP were analyzed for fat (Hooi et al. 2004), protein (AOAC, 2000;method 991.20;33.2.11), total solids (TS) (AOAC, 2000;method 990.20;33.2.44), and ash content (AOAC, 2000;method 945.46;33.2.10).

| Manufacture of LFIC mix
The LFIC mix was formulated to have 3% fat (fat source was buffalo milk, Animal Production Farm, Faculty of Agriculture, Al-Azhar University), 14% milk solids nonfat (SNF) (skim milk powder, Dairy America, local market), 15% sucrose (local market), 0.3% stabilizer (high viscosity minimum assay 95.5% carboxy methyl cellulose, Misr Food Additives), and 0.1% vanillin (local market). The LFIC mix was produced as shown in Figure 1. A 3kg batch of LFCI was prepared from each formulation. All ingredients used to produce LFIC formulations are shown in Table 1. Three different levels of DFP were used in the LFIC mix as follows: 1.5% (T1), 2.5% (T2), and 3.5% (T3). Fresh buffalo milk, skim milk powder (SMP), and DFP were mixed, heated at 85°C for 15 min, following by cooling at 4°C. Meanwhile, sucrose and stabilizer were solved in 85°C water for 15 min, then cooling at 4°C. After that, both blends were mixed evenly to get the LFIC ready. The LFIC was manufactured three times using DFP.

| Analyses of LFIC mix
The ice cream mix was analyzed for relative viscosity (Arbuckle, 1986b) and density (Equation 1). The weight per gallon (lb) was also calculated in the mix as described by Arbuckle (Arbuckle, 1986a) by multiplying the density by the factor of 8.34.
Some microbiological analyses were also performed on the mix.
Total bacterial count (TBC) was enumerated by using the standard plate count technique (Wehr & Frank, 2004). Psychrotrophic bacteria count (PBC) was also enumerated by plating using the SPC procedure and incubating for 10 days at 7°C (Wehr & Frank, 2004).
The coliform count was determined on MacConkey broth media, and tubes were incubated at 32°C ± 1°C for 24 hr (Ashenafi, 1990).
Yeast and mold count were also enumerated (Wehr & Frank, 2004) using potato dextrose agar media, and plates were incubated at 25°C ± 1°C for 5 days.
The whipping of the mix was applied (Mantematic 3/Cattabriga) at 4-5°C, then freezing. The final LFIC products were stored at −18°C for 30 days and examined for physicochemical, microbiological, rheological, and sensory properties.

| Analyses of final LFIC
Density and weight per gallon (lb) were measured in the final LFIC product as described in the mix. The melting resistance of LFIC (Arbuckle, 1986b) and overrun (Arbuckle, 1986b;Gheisari et al., 2020;Muse & Hartel, 2004) was also determined. Additionally, the TBC, PBC, coliform, and yeast and mold were also enumerated in the final LFIC.
The sensory characteristics of LFIC samples were evaluated according to 10-15 trained panelists from the Dairy Science Department, Al-Azhar University. The LFIC was examined as described by Arbuckle with some modifications (Arbuckle, 1986c).
Samples were evaluated for color and appearance (20 points), flavor (30 points), melting quality (20 points), and body and texture (30 points) to have 100 points overall. This experiment was performed in triplicates. DFP concentration and storage time on the characteristics of LFIC.

| Statistical analysis
Mean separation was done using the least significant difference (LSD) comparison test when significant differences were detected at p < .05.

| Formulations of LFIC
Formulations of LFIC were calculated using TechWizard software (Excel-based formulation software).

| Rheological properties of LFIC mix
The data presented in Table 3 exemplified the rheological properties (relative viscosity, density, and weight per gallon) of LFIC mix prepared using DFP at a rate of 1.5%, 2.5%, and 3.5%. Addition of DFP improved the functionality of the mix, which increased the relative viscosity, density as well as weight per gallon compared to control. The relative viscosity increased two times (1.47 in control vs. 3.33 in T1) after adding 1.5% DFP in the LFIC mix. Increasing the DFP concentration to 3.5% led to increasing the relative viscosity, density, and weight per gallon by 5.91, 1.42 g/cm 3 , and 11.88 lb, respectively. Gheisari found that the addition of date to ice cream formulations led to an increase in the viscosity due to the high-fiber content in date (Gheisari et al., 2020).

| Microbiological analyses of LFIC mix
Data presented in Table 4

| Rheological properties of the final LFIC
The data presented in Table 5 exemplified the density, weight per gallon, and overrun in the final LFIC prepared using DFP. There were significant increases (p < .05) in density and weight per gallon (lb) with elevating the concentration of DFP, which is similar to the trend in the mix (Table 3). The density of control LFIC was 0.62 g/cm 3 , and this value increased to 0.80, 0.95, and 1.08 g/cm 3 after addition of 1.5%, 2.5%, and 3.5%, respectively. The weight per gallon also increased from 5.21 lb in control to 6.71 lb in T1, 7.93 lb in T2, and 9.02 lb in T3. However, overrun decreased (p < .05) to 36.87, 29.70, and 24.04 after addition of 1.5%, 2.5%, and 3.5% DFP, respectively, compared to 50.0 in control. The overrun is referred to as the ability of ingredients and mix to retain air bubbles, which revealed that DFP has a lower ability to retain air bubbles.
The density, weight per gallon, and overrun of LFIC improved with the addition of DFP. Similar results for control were reported in other studies (Arbuckle, 1986b;Muse & Hartel, 2004).
The functionality of fiber could increase water-binding amplitude and thickness of ice cream, which in turn, led to an increase in the density and weight per gallon of LFIC (Staffolo et al., 2004). It also may be related to the difference in moisture content of LFIC mix.
Remarkably, the addition of 3.5% of DFP increases the density and, weight per gallon, and decreases overrun by twofold compared to the control. The interaction between fiber and protein can lead to improvement.
The melting resistance of LFIC made with DFP is shown in Figure 2. The melting characteristics of LFIC showed significant differences (p < .05). The melting property of LFIC after 10 min at 37°C was 3.66%, 2.95%, and 1.92% for the LFIC containing 1.5%, 2.5%, and 3.5% DFP, respectively, while 14% of control ice cream was melted after 10 min. It was expected that increasing the time would lead to elevate the melting area of LFIC. The control ice cream was melting fast as compared to LFIC made with DFP after 10, 20, 30, 40, and 50 min, which means that DFP is increasing the melting resistance. These melting values increased to 41.88%, 42.33%, and 38.95% after 40 min for the LFIC containing 1.5%, 2.5%, and 3.5% DFP, respectively, compared to 82% in control.
The control ice cream was completely melted after 50 min, while 74.85%, 69.44%, and 63.30% of T1, T2, and T3, respectively, were melted. The differences in melting resistance between control and DFP ice cream are contributed to freezing points and viscosity of LFIC that was affected by the addition of DFP.
The melting resistance was improved with the addition of DFP.
The result shows an inverse relationship between melting resistance and overrun. Similar results were reported in another study (Sakurai et al., 1996). One of fiber functionality is increasing the waterbinding that delays melting point (Staffolo et al., 2004). The amount of air incorporated and fat percentage can affect the melting resistance (Muse & Hartel, 2004).   It has been reported that the addition of date pulp to ice cream formulations did not affect the flavor (Gheisari et al., 2020). The lower flavor score of LFIC with the addition of DFP could be related to the growth of ice crystals (Schaller-Povolny & Smith, 1999). The addition of fiber has decreased the flavor score of ice cream comparing to control (Crizel et al., 2014). It may contribute to acidity values produced from additive fiber during storage time (de Moraes Crizel et al., 2013). The body and texture of LFIC were improved with the addition of DFP that related to decreasing the ice by improving the capacity of water-binding (Soukoulis et al., 2009). The LFIC made with DFP was acceptable with high overall scores, which was similar to a previous study (Gheisari et al., 2020).

| CON CLUS ION
The addition of DFP at a level of 1.5%, 2.5%, and 3.5% improved the density, weight per gallon, and melting resistance of LFIC. Additionally, DFP improved the sensory characteristics of LFIC, including body and texture, melting quality, and appearance as compared to control during 30 days of storage at −18˚C. DFP is a suitable and cheap ingredient that can be used as a valuable source of fiber in ice cream formulations. DFP has more benefits from nutritional and technological aspects. DFP can replace the fat in ice cream formulations to produce LFIC with characteristics relatively similar to those in full-fat ice cream.

DATA AVA I L A B I L I T Y S TAT E M E N T
Research data are not shared.