Ah, the topic of animal feeding by visitors in zoos-a subject that has engaged zoos for several decades now. Over the years, the attitude has changed from "Feed whatever You want to whatever You want" to "Do Not Feed the Animals" or only selected feeding (petting zoos, deer gardens, keeper talk etc.).
There are several reasons why nowadays most zoos prohibit the feeding of zoo animals (nevertheless, a lot of zoo animals end up each year on the surgery or necropsy table because of feeding by visitors). The most important issues are veterinarian/general husbandry concerns (zoonosis transfer, adipositas, control of the amount and quality of food taken in by the individual, guarantee of apt food, prevention of foreign body intake, increased aggression of animals against each other and visitors out of greed, increased accident risk etc.), but also other aspects (begging animals are no longer "PC"...) are taken here into account. And if You remember the constant reports about stupid visitor behaviour, which fill more than one thread here, one can understand why zoos don't want to face an unnecessary risk here.
On the other hand, the feeding of animals is a rare and great opportunity for direct animal-contact-a very important aspect in the self-acclaimed role of modern zoos as nature-mankind-interface. Additionally, responsible (ha, a good joke...) feeding by the visitors would also have the affect of dividing the meal for the animal into several small parts a day, instead of one or two "big meals" a day. This can be both beneficial in terms of a better digestion as well as crucial in lowering stereotypical behaviour in some cases (as recent studies show that irregular feeding at varying intervalls a day can significantly decrease stereotypical behaviour in some specimens). However, I wouldn't count on the latter...
Hamburg Zoo is still a private business and needs all the money they can get-including animal food sales. The problem of this recently made the news due
that orang-utan drowning in the attempt to reach food offered by a visitor...
In conclusion, animal feeding in zoos is a mixed blessing. Most veterinarians, keepers and curators would be happy if they did not have to mourn about a visitor-feeding related animal loss, while the visitors and the animal food salesmen would love to return to the old "Feed whatever.." motto. So what? I wouldn't ask the animals themselves, though, as the answer ("Gimme me food") would be rather predictable in some cases...My suggestion: why not feed the zoo staff instead? Preferably delicatessen and first-class beverages; Whole Foods products now and then might do, too...
Finally, I would like to remember some old allegations that came up when Frankfurt Zoo (under Grzimek) abolished the feeding of the animals by visitors; according to the "experts" back then, this would result in the ultimate downfall of zoos, as no one would then visit a zoo if not being allowed to feed the animals...

Yes, the Times They Are a Changin'....