To enable the use of anthocyanins in food with high oil content, bilberry anthocyanins were acylated with cinnamic acids to address their poor lipid solubility. Structural analyses based on Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and 1 H nuclear magnetic resonance analyses indicated that cinnamic acids were efficiently grafted onto 6-OH of glucoside and galactoside and 5-OH of arabinose through an esterification reaction. The higher the dose of the acylating agent, the higher the acylation degree (AD) and the lower the total anthocyanidin content (TAC) of bilberry anthocyanins. An-Ci4 presented the highest AD value (6.61%), and An-Ci3 exhibited the lowest TAC value (50.16 mg/g). After acylating with lipophilic cinnamic acids, the lipid solubility of acylated bilberry anthocyanins significantly improved. The color of the native bilberry anthocyanin solution dissolved in ethyl acetate and dioxane was transparent. By contrast, the acylated anthocyanin solution dissolved in these solvents was unmistakably red. In terms of the antioxidant activity, acylated bilberry anthocyanins demonstrated inferior performance in 2,2-diphenyl-1-picrylhydrazyl (DPPH) clearance but a better inhibition ratio in β-carotene bleaching assay compared with native bilberry anthocyanins. As AD value increased, the DPPH clearance of acylated anthocyanins decreased and their inhibition ratio increased in β-carotene bleaching assay.

The retrieval practice effect refers to the fact that one or even multiple retrievals of memory content during the same period are more effective than repeated studying to promote future memory retention. It is effective for numerous declarative knowledge learning materials. However, studies have demonstrated that retrieval practice does not benefit problem-solving skill learning. This study used worked examples from math word problem tasks as learning materials, considering the retrieval difficulty as the main factor. Experiment 1 explored the effect of retrieval practice on acquiring problem-solving skills under different initial testing difficulties. Experiment 2 manipulated the difficulty of materials as a variable to ascertain the effect of retrieval practice on problem-solving skills under different material difficulty levels. Experiment 3 introduced feedback variables to facilitate the generation of the retrieval practice effect and examined the effects of various difficulty feedback levels on problem-solving skills learning. Results showed that, compared with restudying examples (SSSS), the example-problem pairs (STST) did not promote delayed test performance. As for the retrieval practice effect, as no differences or advantages were found in the repeated study group on the immediate test, the retrieval practice group generally outperformed the repeated study group on the delayed test. However, across the three experiments, we found no evidence of retrieval practice affecting results during an enhanced delayed test. Therefore, there may be no retrieval practice effect on acquiring problem-solving skills from worked examples.