# build inverse hash, if all values are unique
my %inverse_hash;
for my $key (keys %hash) {
	for my $val (@{ $hash{$key} }) {
		$inverse_hash{$val} = $key;
	}
}

# debug: inspect the converted data
print Dumper(\%inverse_hash);

# lookup is simple!
print $inverse_hash{banana}, "\n";