Conclusion
The thermal treatment significantly influenced the physicochemical,
structural, functional and digestibility properties of protein in walnut
kernel flour in a temperature-dependent action. SEM micrographs reveled
the walnut kernel flour by roasting and steaming treatment more
sensitive
than the untreated, while the steam treatment had more influence on
walnut kernel flour than the roasting treatment. The secondary
structures of protein in walnut kernel flours were affected by heating
as measured by FTIR, the protein structure changes of samples for
steamed processing happened to a greater extent than that of roasted
ones. It was found that the heat treatment could result in unfolding of
protein, which had significantly affected the functionality of samples.
The results showed that the roasting and steaming treatment affected the
amino acid composition and amino acid score (AAS), such as the roast
processing decreased the AAS for essential amino acids compared to the
untreated sample, while the steam processing increased the AAS. But the
lysine was the only limiting amino acid for all samples.
It was noted that the digestibility, water holding capacity and oil
holding capacity, foaming and emulsion capacities and stabilities of
walnut kernel flour during heat processing increased compared to
untreated, however, with the extension of heating time, these functional
properties would produce the different changes. At the same time, the
walnut kernel flours prepared by heating treatment were characterized by
high enthalpy (△H), storage modulus (G′), loss modulus (G′′) and
viscosity compared to that of untreated sample, the order of these
values from high to low was the steaming > roasting
> untreated. Therefore, it could conclude that when the
heating technique would be used to alter the functional properties and
quality of walnut kernel flour and considered to have good utilization
promises in food industry. Further, it was proved that the moisture
pretreatment due to containing water in the modifications of functional
properties and quality of protein based on food materials was more
effective than dry-heating.
Author Contribution Xiaoyan Zhao : Project administration,
Resources, Supervision, Funding acquisition, Writing – review &
editing. Haifang Hu : Project administration, Resources,
Supervision, Funding acquisition. Xiangrui Ren : Investigation,
Writing – original draft. Xiaowei Zhang : Data curation,
Methodology, Writing - original draft. Hongkai Liu :
Conceptualization, Software. Meng Wang : Validation, Formal
analysis.
Acknowledgments Financial support of this work by National
Natural Science Foundation of China (Grant No. 21406133) and Xinjiang
Key Scientific and Technological Project (Grant No. 2021A02002-2).
Data availability Xiaoyan Zhao can be contacted for the data
Conflict of Interest The authors declare that they have no
known competing financial interests or personal relationships that could
have appeared to influence the work reported in this paper.