Plants also differ in their palatability to herbivores. Protein powders are the most popular and may have flavoring added for palatability. Starch content (amylose) of rice is very important factors in grain yield, processing and palatability. Umami enhances the palatability of a wide variety of foods. Opioid receptor-related processes in the nucleus accumbens and ventral pallidum affect the palatability of foods. Cultivars may be selected for yield, palatability for livestock, and drought resistance. Yudkin refers to these developments as the separation of palatability from nutritional value. Food reinforcement is influenced by several factors including food palatability, food deprivation, and food variety. Sometimes molasses is added to improve palatability. It is used in cat foods as a palatability additive. Gastrostomy feeding avoids any issues with palatability, and bottle-fed infants readily accept the ketogenic formula. Endozoochory syndrome characteristics will develop based on palatability of the fruit by an organism. McCollum decided that some diets failed because they lacked "palatability". Even among the edible species, the palatability of the flesh varies from species to species. He found that glutamate was responsible for the palatability of the broth from "kombu" seaweed.