Or HaChaim on Genesis 41:48/אור החיים על בראשית מ״א:מ״ח

1 ויקבץ את כל אכל, He collected all the food, etc. According to the commentary on verse 34 that the word וחמש meant setting aside a tax of 20% the words "all the food" refer to the king's share. According to the alternative commentary that the word וחמש means lending a sense of urgency to the measures to be taken, the verse may be explained literally; Joseph collected the entire excess of that year's harvest over average years' harvests. He bought up all the excess. The farmers offered it for sale seeing they had no use for it.