Increased stored soybean dietary fibre concentration is positively correlated to testa darkening measured chromaticity

• Understand the behaviour of soybean grains during storage.
• Storage related soybean testa darkening measured and reported via the C*ab method.
• Storage related increase in soybean insoluble and soluble dietary fibre is measured.
• Proposed relationship between soybean testa darkening and increased dietary fibre.
• The mechanism for soybean fibre increase is discussed and elucidated.

To assess efficacy of seed testa chromaticity indicator of dietary fibre changes in soybean (Glycine max L.), soybean samples were stored for zero (0 M), three months (3 M), six months (6 M) or nine months (9 M) at three moisture contents (MC) (9, 11 and 13%) and three temperatures (10, 20 and 30 °C). Stored soybean samples were analysed for seed testa colour and dietary fibre content. Extended storage (9 M) at high MC (13%) and temperature (30 °C) resulted in reduced chromaticity (C*ab) and L* (darkening) of the testa colour value by 6.7% and 4.7% respectively. Furthermore, storage time and elevated MC (13%) had the biggest effect on dietary fibre levels with insoluble and soluble dietary fibre increasing significantly up to 9 M of storage, by 4.90% and 15.09% respectively with a total dietary fibre increase of 4.62%. This effect was enhanced with increased storage time. Use of testa colour as an indicator of the effect of storage time and conditions on soybean dietary fibre levels contributed to understanding the related impact on the nutritional quality of soybean. This study elucidated the role of post-harvest storage time and conditions on soybean dietary fibre levels as related to chromaticity.