| Sucrose(SUC)is the most commonly used added sugar in candied fruit processing,adding sweetness while giving the product fullness and a firm texture.Nowadays,the demand for sweetness is reduced in the context of sugar reduction,so the question of how to improve the texture of candied fruits with reduced sugar has become a central issue.In this paper,Monterey strawberry(Fragaria × ananassa Duch)was used as the raw material.The effect of four SUC alternate sugars,isomaltooligosaccharide(IMO),trehalose(TRE),sorbitol(SBT)and erythritol(ERT),on the texture of candied strawberries by solid osmotic dehydration(SSD)in a single or combined manner was investigated.Then two groups of SSD formulations for sugar-reduced candied strawberry were obtained by mixing experimental design.Finally,the quality of the reduced-sugar formulation was evaluated in comparison with SUC candied strawberries from two perspectives:quality during storage and pectin simulation system.The results provide a method and data basis for the development of sugar-reduced candied strawberries.The main research results are as follows:(1)Different sugars/sugar alcohols had different effects on strawberries with SSD.The solids gain(SG)of SUC-treated strawberry samples was significantly higher than that of the ERT,TRE,SBT,and IMO groups(P<0.05),and water loss(WL)was IMO,SBT,TRE,ERT,SUC in descending order.To obtain candied strawberries with 20%moisture content,the time required for the five sugars/sugar alcohols SUC ≈IMO>TRE≈SBT>ERT,and ERT shows the worst water holding capacity.The results of digital microscopy and PAS staining of candied strawberries cross-sections showed that the candied strawberries made by TRE,ERT,and SBT alone showed crystalline antisanding appearance and uneven distribution of internal pores,while the candied strawberries made by IMO alone showed tightness and dryness both inside and outside.The experimental design of mixing four sucrose substitutes using Design-Expert software revealed that there were significant interactions(P<0.05)between two sugars IMO and TRE and between three sugars/sugar alcohols IMO,TRE and SBT affecting the hardness and elasticity of the candied strawberries,and finally this was used to obtain the reduced sugar formulations for strawberry SSD treatment with suitable hardness and maximum elasticity,the first group The first group was IMO+TRE+SBT(IMO:TRE:SBT=60:20:20)with hardness 178.25 g and elasticity 0.37 g.The second group was IMO+TRE(IMO:TRE=75:25)with hardness 150.15 g and elasticity 0.37 g.The sugarreduced strawberry candied strawberry formulations were full and shiny in appearance,with regular internal cell wall structure and uniform distribution of alternative sugars.(2)In order to evaluate the differences in quality changes between the two formulations and SUC candied strawberries during storage,the moisture content,moisture distribution and migration characteristics,color,TPA texture,total sugar,ascorbic acid,total phenolic content and sensory were measured during 4 months of storage.The results showed that the moisture content of the SUC,IMO+TRE and IMO+TRE+SBT formulations decreased from 20%to 18.01%,17.89%and 18.05%,respectively,during the storage up to the 2nd month.In the fourth month of storage,the moisture content of the three types of candied strawberries showed an increasing trend,and the low-field NMR results at this time showed that the peak area A21 value was the highest and the relaxation time T21 value was lower in the formula candied strawberries,and the moisture migrated in the direction of lower freedom,while the T21 and A21 values of moisture in the SUC candied strawberries became 0 and the T22 region exhibited the largest peak area,so the formula candied strawberries had a more stable moisture status.During storage,the total sugar content of reduced-sugar dried strawberries was significantly lower than that of SUC dried strawberries(P<0.05).There was no significant difference(P>0.05)in color index between the three candied strawberry at storage up to the 0th and 4th month.The hardness,elasticity,Vc and total phenolic content of the three types of dried strawberries showed similar trends during storage and were not significantly different(P>0.05).Finally,the sensory evaluation revealed that the scores of candied strawberries of IMO+TRE+SBT formulation were not significantly different from those of SUC candied strawberries(P>0.05)and were significantly higher than those of IMO+TRE formulation(P<0.05).Therefore,the IMO+TRE+SBT formulation is more suitable for making candied strawberry instead of SUC,and the difference in moisture status may be a key factor in analyzing the difference in quality of the three candied strawberry.(3)A strawberry pectin gel simulation system was established to evaluate different sugar/sugar alcohol formulations.The effect of different sugars/sugar alcohols or their combinations on the formation of strawberry pectin gels was investigated:during the drying process and the sugar/sugar alcohol concentrations were determined,and the water distribution(A2)and relaxation state(T2)of the process were monitored by low-field NMR.The hardness,FTIR,XRD,DSC and rheological properties of the strawberry pectin gels were also measured to analyze the effect of different sugars/sugar alcohols or their combinations on the properties of the simulated system.The results showed that the T2 turning point transition times of the pectin solutions of SUC,IMO,TRE,SBT,IMO+TRE formulation and IMO+TRE+SBT formulation occurred at 270 min,255 min,267 min,319 min,266 min and 250 min,respectively,and the different sugar/sugar alcohol combinations affected the onset of the gel turning point;in addition,the IMO+TRE+SBT formulations had lower T2 compared to lower sugar/sugar alcohol concentrations,indicating that the IMO+TRE+SBT formulations at lower sugar/sugar alcohol concentrations could form gels with lower sugar and more stable moisture state.The rheological measurements showed that the gels made with different sugars/sugar alcohols exhibited colloidal behavior,and the viscosity of the pectin gel of the IMO+TRE+SBT sugar/sugar alcohol formulation was closest to that of the sucrose pectin gel;compared to SUC,the IMO+TRE+SBT formulation was more likely to exhibit greater elastic strength.In terms of hardness,there was no significant difference between the IMO+TRE+SBT formulation,IMO+TRE formulation and SUC strawberry pectin gels(P<0.05).On XRD patterns,SUC strawberry gels showed crystallinity,while both IMO+TRE+SBT and IMO+TRE formulations strawberry gels did not.The FTIR spectra showed that the IMO+TRE,IMO+TRE+SBT formulations and SUC strawberry pectin gels produced close peak intensities in the 2933 cm-1 and 800-1300 cm-1 regions,which may become one of the reasons explaining the ability of these three to be similar in hardness and viscoelasticity.This simulation system clearly explains the effect of the combination between sugar/sugar alcohols on the formation and gel texture of strawberry pectin gels,and the experimental results provide new ideas for the study and texture evaluation of candied fruits. |
