Regulating endosperm composition of rice through nutrient management for improved taste

  Objectives  We studied the effects of different nutrients on the endosperm composition of rice, in order to improve the taste of rice through fertilization.

  Methods  Field experiments with orthogonal experimental design of four-factors at three levels L₉(3⁴) were conducted in Shenyang, Liaoning Province. The four factors were rice cultivar, phosphate (P), potassium (K), and magnesium (Mg) fertilizer rate. The three rice cultivars included a soft rice cultivar with low apparent amylose content (AAC), a common Japonica cultivar and a high-yielding japonica cultivar. The amylose and protein contents in different layers of rice flour were analyzed, and the relationship between fertilizer rate, taste and texture characteristics was investigated.

  Results  From the taste performance, the soft rice variety with low amylose content was the best, followed by the high-yield strain Yanjing 4. Different endosperm components in different layers had different effects on texture and taste characteristics. The flavor layer AAC dominated the gelatinization characteristics and core layer AAC dominated the palatability. The protein content in outer layers greatly influenced the RVA and the taste characteristics, which is responsible for the taste in the flavor layer. Path analysis showed that the balance, viscosity and adhesiveness of surface texture had the highest direct effect on the taste, and the effect was mainly adjusted by the balance. For overall texture, the taste value was influenced by the viscosity and hardness, and the adhesion amount contributed tremendously to the taste value. High P application rate reduced AAC and hardness, and high K application rate effectively improved AAC of soft rice and promoted protein synthesis whereas, high Mg application rate significantly improved the viscosity, adhesive characters and palatability of rice. In terms of RVA, high P + medium or high Mg fertilizer was the basis of increasing breakdown value and decreasing setback value in the formula fertilization combination. In terms of texture, high Mg fertilizer combined with different levels of P and K fertilizer could improve texture adhesion properties of rice, and high K fertilizer was the basis for improving surface viscosity and balance of rice. However, for soft rice cultivar, the content of amylose and protein could be increased by applying K and Mg fertilizer in moderate amount, combined with higher level of P fertilizer, so as to achieve the best taste. Common cultivar required reduced K fertilizer to increase viscosity.

  Conclusions  Fertilizer rate influences taste by regulating endosperm composition. P application mainly improves the appearance and taste of rice, K application has obvious effect on texture characteristics, and Mg application enhances palatability. High P + high K + high Mg rates are more suited for organoleptic quality of soft rice cultivar, and high P + low K + medium or high Mg rate is the best fertilizer combination for common rice cultivar.