The effect of particle size distribution on fat bloom and quality in stearine and olein based chocolates

In this study, milk chocolate samples containing commonly used cocoa butter substitutes (CBS), hydrogenated palm kernel olein (HPKO), and stearin (HPKS) were prepared using a ball-mill system to achieve different average particle sizes (D90) of 20.0, 25.0, 30.0, 35.0, and 40.0 μm. HPKS samples showed lower moisture levels than HPKO samples (p<0.05), although no significant relationship between average particle size and moisture content was found for either group. Water activity values ranged narrowly between 0.250 and 0.262. Hardness values (4239.3-5691.4 g) were measured using the penetration technique. HPKO samples did not show significant changes in hardness with particle size, while HPKS samples showed increased hardness with larger particle sizes (P<0.05). The study also examined the effects of palm oil type and average particle size on color properties, determining L* (32.93-35.48), a* (8.43-8.81), b* (10.33-11.13), chroma (13.31-14.23), and hue angle (50.77-51.58) values. HPKS samples showed increases in a* and b* values with larger particle sizes. Sensory attributes (color, brightness, initial bite hardness, crumbliness, smoothness, waxiness, flavor, melt-in-mouth) were evaluated by chocolate technology experts. No significant differences were found for attributes other than smoothness and flavor, which decreased in preference with increasing particle size for both HPKS and HPKO samples (P<0.05). An accelerated shelf life (ASL) study was conducted with 99 cycles of temperature changes (20°C and 30°C) at 45% relative humidity for 6-hour intervals. Water activity values remained below 0.400 at the end of ASL. During storage, hardness initially increased but decreased in the later stages due to increased moisture levels. Color measurements and whiteness index (WI) values were recorded during ASL. HPKS samples maintained a ΔE value below 2, while HPKO samples exceeded 3 when particle size was below 30.0 μm. HPKO samples with particle sizes above 30.0 μm showed more stable color changes. WI values ranged from 30.6 to 33.1 for HPKS samples and from 36.4 to 38.2 for HPKO samples, with HPKS samples having lower WI values due to their higher SFC ratio. The study concluded that HPKS has advantages in quality and stability, while particle size effects are generally negligible outside of sensory properties.