title: Porosity and water activity effects on stability of crystalline β-carotene in freeze-dried solids.
abstract: Stability of entrapped crystalline β-carotene as affected by water activity, solids microstructure, and composition of freeze-dried systems was investigated. Aliquots (1000 mm(3) , 20% w/w solids) of solutions of maltodextrins of various dextrose equivalents (M040:DE6, M100:DE11, and M250:DE25.5), M100-sugars (1:1 glucose, fructose and sucrose), and agar for gelation with dispersed β-carotene were frozen at -20, -40, or -80 °C and freeze-dried. Glass transition and α-relaxation temperatures were determined with differential scanning calorimetry and dynamic mechanical analysis, respectively. β-Carotene contents were monitored spectrophotometrically. In the glassy solids, pore microstructure had a major effect on β-carotene stability. Small pores with thin walls and large surface area allowed β-carotene exposure to oxygen which led to a higher loss, whereas structural collapse enhanced stability of β-carotene by decreasing exposure to oxygen. As water plasticized matrices, an increase in molecular mobility in the matrix enhanced β-carotene degradation. Stability of dispersed β-carotene was highest at around 0.2 a(w) , but decreasing structural relaxation times above the glass transition correlated well with the rate of β-carotene degradation at higher a(w) . Microstructure, a(w) , and component mobility are important factors in the control of stability of β-carotene in freeze-dried solids.
  
  
  CONCLUSIONS
  β-Carotene expresses various nutritional benefits; however, it is sensitive to oxygen and the degradation contributes to loss of nutritional values as well as product color. To increase stability of β-carotene in freeze-dried foods, the amount of oxygen penetration need to be limited. The modification of freeze-dried food structures, for example, porosity and structural collapse, components, and humidity effectively enhance the stability of dispersed β-carotene in freeze-dried solids.
authors.affiliation: Department of Food Science and Technology, Kasetsart University, Thailand.
authors.forename: Nathdanai
authors.initials: N
authors.lastname: Harnkarnsujarit
authors.forename: Sanguansri
authors.initials: S
authors.lastname: Charoenrein
authors.forename: Yrjö H
authors.initials: YH
authors.lastname: Roos
mesh_terms: D002152:Calorimetry, Differential Scanning; D003080:Cold Temperature; D003116:Color; D003460:Crystallization; D005511:Food Handling / Q000379:methods; D063427:Food Quality; D061353:Food Storage; D005612:Freeze Drying / Q000379:methods*; D005632:Fructose / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D016014:Linear Models; D016062:Porosity; D013395:Sucrose / Q000737:chemistry; D014867:Water / Q000737:chemistry*; D019207:beta Carotene / Q000737:chemistry*
chemical_list: D019207:beta Carotene; D014867:Water; D005632:Fructose; D013395:Sucrose; D005947:Glucose