This is very interesting Mr. Pankaj Yadav

The higher incidence of rotting in large bulbs may be attributed to higher water content. Moreover, the sprouting of larger sized bulbs in storage may also be attributed to the late time of harvesting. The colour of the outer scale is correlated with the storability of the onion. The onion bulbs with high pyruvic acid content have better storage quality. The red onion varieties have higher phenolic compounds than the white varieties, which protect them against pathogenic infection, and thus have a better keeping quality. Light red-coloured onions were found to have a lower respiration rate while comparatively higher respiration rate was found in dark red and white-coloured varieties. These show that colour and bulb size likely have an influence on storability/ shelflife of onion, however, it seems also other factors associated with postharvest and storage are attributing the storability of onion bulbs.

Dear Pankaj Yadav you may also see:

WARD, C. M. (1979). The effect of bulb size on the storage-life of onions. Annals of Applied Biology, 91(1), 113–117. doi:10.1111/j.1744-7348.1979.tb07420.x

Isma’ila M, E. Karu, D. A Zhígila, Yuguda U. A. Postharvest Storage and Shelf Life Potentials among Selected Varieties of Onion (Allium cepa L.). Scholars Academic Journal of Biosciences, 2017; 5(4): 271-277.

DOI: 10.21276/sajb.2017.5.4.3

Tripathi, P. C., & Lawande, K. E. (2019). Onion storage in tropical region—a review. Current Horticulture, 7(2), 15-27. DOI: 10.5958/2455-7560.2019.00014.1

Fruit size is determined by the total number of cells and their expansion in the fruit. If the fruit size increase due to the increase in the number of cells, the spaces between the cells will be less. But if it increases as a result of a cell over-expansion, the spaces between cells will be more. In general, as the space between cells increases, compactness of the fruit is lost and the storage life decreases.

It is not correct to establish a correlation between color and storage time because it is the genetic characteristic of the variety, not the color that determines the storage life. Possibly, pink and light red colored onions has a different cellular structure compared to white and dark red colored varieties.

Thanks a lot dear Hayri Ustun for your notable answer.

It might b due to presence or absence of some plant harmone or pigment. Water content also determines life of vegitables and fruits. More water content is inversly proportional to storage life.

Thanks a lot dear Mubashir Ali Rather for your notable point

This is very interesting Mr. Pankaj Yadav

The higher incidence of rotting in large bulbs may be attributed to higher water content. Moreover, the sprouting of larger sized bulbs in storage may also be attributed to the late time of harvesting. The colour of the outer scale is correlated with the storability of the onion. The onion bulbs with high pyruvic acid content have better storage quality. The red onion varieties have higher phenolic compounds than the white varieties, which protect them against pathogenic infection, and thus have a better keeping quality. Light red-coloured onions were found to have a lower respiration rate while comparatively higher respiration rate was found in dark red and white-coloured varieties. These show that colour and bulb size likely have an influence on storability/ shelflife of onion, however, it seems also other factors associated with postharvest and storage are attributing the storability of onion bulbs.

Dear Pankaj Yadav you may also see:

WARD, C. M. (1979). The effect of bulb size on the storage-life of onions. Annals of Applied Biology, 91(1), 113–117. doi:10.1111/j.1744-7348.1979.tb07420.x

Isma’ila M, E. Karu, D. A Zhígila, Yuguda U. A. Postharvest Storage and Shelf Life Potentials among Selected Varieties of Onion (Allium cepa L.). Scholars Academic Journal of Biosciences, 2017; 5(4): 271-277.

DOI: 10.21276/sajb.2017.5.4.3

Tripathi, P. C., & Lawande, K. E. (2019). Onion storage in tropical region—a review. Current Horticulture, 7(2), 15-27. DOI: 10.5958/2455-7560.2019.00014.1

The onion storage depends on genetic, nutrition and also treatment harvesting. Potassium, Calcium fertilizers improve storage time.

coloured onions has longer shelf life may be due to the presence of some pigments present in them while small size onion stored longer due to the surface area to volume ratio of the bulb.

Thanks a lot dear professor Abdul Jafari Shango , Ahmad Ajani , Mohammed Ahmed for your notable point it will sure helps in my further research work.

Definitely.

Because of the increased pungency in the onions

Thanks a lot dear Ahmad Ajani , A. M. A. El-Anany for your answer

Small onions have cells with compact cell internal so, they maintain less water than the big ones. This is not good for long term storage.

I thing white and dark red varieties have high sugar content (May not necessary true). Large varieties usually grow fast and they have high moisture content. When they are stored they lose their moisture and shrink. Besides, well dried bulbs with closed necks can be stored longer. During harvest if your produce is mixed, the small bulbs remain dry and have closed necks. I think comparison should be made based on their size.

Thanks, dear professor Ahmad Ajani for your answer

Thanks a lot, dear professor Bekele Abebie for your wonderful answer.

I experienced that it's very good treatment to don't remove the onion leaves after harvesting immediately. This help to transfer the remains assimilates leave to the onions. Also, the onion neck become closed more. All of this are useful for long term storage.

Coloured onions have pigments that help protect the plants and delay oxidative processes, while bigger ones have high moisture content and loose cell arrangement. The high moisture content in big onion could also mean dilution of pigments; hence lower conc of pigments in large onion than in small ones.