Solving the Problem of Hard Seeds

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Hard seed, partially-hydrated seed and fully-hydrated seed in pinto bean grown in 2015 on the Prairies. (PHOTO: Parthiba Balasubramanian)

Beans are primarily sold as a dry commodity, and therefore, visual seed quality is important – an intact seed coat, along with uniform colour, size and shape. However, it’s seed coat and colour that matters most in cooking and canning, the primary end-uses of beans.

“We have come across bean lines with poor seed coat integrity, which means hairline cracks, breaking and so on,” notes Parthiba Balasubramanian, a research scientist at the Agriculture and Agri-Food Canada (AAFC) Research and Development Centre in Lethbridge, Alta. “If the seed coat integrity is compromised, beans tend to lose starch during canning, and this may lead to clumping of bean seeds at the bottom of the can. Bean seeds can also lose colour during soaking, blanching, cooking and canning.”

In addition, some seeds do not absorb water at all (known as “hard seeds”) or only partially absorb water during soaking (resulting in a wrinkled seed coat). Obviously for canning companies, the fewer of these seeds, the better. Indeed, in terms of hydration, processors and consumers prefer beans to double in weight after soaking.

Balasubramanian notes that while standard blanching in a canning plant (a heat treatment of three minutes at 93 C) is most often sufficient to fully “plump up” hard seeds, some require a heat treatment of 20 minutes at 95 C for complete hydration. Because of this, canning companies usually remove all seeds that do not hydrate or partially hydrate after soaking before the blanching stage, and therefore lose money on them.

Balasubramanian has been investigating the processing traits of lines of various classes of beans since 2011. Experimental lines identified with good cooking and canning quality attributes will go on to possible registration for commercial use in Canada.

“Our results will assist the Registration Recommending Committees (Ontario Pulse Crop Committee and Prairie Recommending Committee for Pulse and Special Crops) in assessing the merit of experimental lines prior to registration as cultivars,” Balasubramanian notes. “The results will help growers in choosing cultivars with good quality attributes, and bean dealers in choosing cultivars when contracting commercial bean production.”

The assessment includes experimental dry bean lines of navy, pinto, black, great northern, red, pink, yellow, light red kidney, dark red kidney, white kidney and cranberry beans. These lines, from both public and private breeding programs across Canada, are compared to their respective “control” or “check” registered cultivars in order to make conclusions about yield, disease resistance and other agronomic traits, as well as quality traits which include the proportion of hard seeds and other traits related to canning.

Jenn Walker, research officer with the Alberta Pulse Growers, notes that while hard seeds are not a major issue for growers because there is no way to visually identify them, “perhaps if science can discover the root causes behind failure to hydrate, there could be ways to mitigate this through agronomy and breeding in the future.”

The experimental lines are from Cooperative Registration trials grown at several locations in Ontario and the three Prairie provinces. Funding for this research was provided at the start through Pulse Cluster 1 (with support from AAFC’s Growing Forward program, Alberta Pulse Growers and Ontario Bean Growers). The work is currently being continued under Pulse Cluster 2 until 2018.

Since 2015, Balasubramanian has also led a small three-year project funded by the Ontario Bean Growers to assess hard seeds in select navy bean cultivars that are commonly grown in Ontario and Manitoba. They are part of Regional Trials of 2015, 2016 and 2017. He says this study enables a look at environmental factors in a comparison of how many hard seeds are present in common cultivars grown at several locations in different geographic regions.

THE RESULTS

In 2015, Balasubramanian noted the highest percentage of hard seeds after soaking (more than 50 per cent) was found to be in a red bean experimental line. He adds there was one navy bean cultivar which consistently had hard seeds and/or partially-hydrated seeds after soaking when grown at a large number of locations (six in Ontario and three in Manitoba).

There were four other navy bean cultivars tested last year, and while they all had hard seeds and/or partially-hydrated seeds, that was not consistently observed at all locations. “In March 2017, we will evaluate four navy bean cultivars grown in Ontario and Manitoba in 2016 to see if the same trend continues.”

So, while genetics may play some role, the fact that Balasubramanian has not consistently observed hard seeds in any given cultivar/experimental line indicates that environmental conditions have a large influence on hard seed development.

“Environmental conditions during seed maturity, and subsequent processing and storage all affect hard seed development, but I have not done any studies looking at these elements so far,” he explains. “I would say that for growers, good genetics in terms of agronomic traits are important, but I would also promote choosing the cultivars best adapted to your specific environment so that you get fully mature seeds. Visually, immature seeds may look normal, but they generally do not absorb water during soaking.”

As to whether cultivars with “good” dry seed characteristics generally have “good” processing traits, Balasubramanian answers yes. “An example can be given from May 2016, when we registered a yellow bean cultivar called AAC Y015 with good seed coat colour,” he says. “Even after canning, this cultivar had significantly better yellow seed coat colour compared to the check cultivar, adding to the visual appeal for the consumers.”

This spring, the Bean Pilot Plant at AAFC Lethbridge received a rotary retort to replace its stationary retort, and staff were trained on how to use it in June. “The new retort has reduced the processing time of bean seeds in cans by approximately 50 per cent,” Balasubramanian notes. “We also hope the new retort will enable us to identify dry bean lines with superior canning quality. We are currently assessing the canning quality of experimental cranberry dry bean lines from the AAFC breeding program, and in November and December, we began receiving seed samples of experimental dry bean lines from Ontario, Manitoba and Saskatchewan for evaluation. Samples of dry bean seeds harvested in 2016 will be the first to be assessed.”

Balasubramanian and his team will continue evaluating dry bean experimental lines from bean breeding programs across Canada for cooking and canning quality attributes up to 2018 and hopefully afterwards. “I anticipate the study will be renewed under the next phase of pulse cluster funding,” he says.