Rashi on Genesis 43:20/רש"י על בראשית מ״ג:כ׳

1בי אדני O, MY LORD — The word בי is an expression of entreaty (בעיא) and supplication. In Aramaic we have בייא בייא “woe, woe!” (Yoma 69b).

2ירד ירדנו WE CAME INDEED DOWN — This is a “come down” (degradation) for us. We have been accustomed to give food to others and now we are dependent upon you (Genesis Rabbah 92:4).