By TMZ Sports

The 'bad blood' angle is being stirred for a planned fight between Floyd Mayweather Jr. and Andre Berto on September 12th at the MGM Grand in Las Vegas.

A few weeks ago, Berto alleged that Mayweather was continuously pranking his cell phone. Berto claimed, to TMZ, that his friendship with Mayweather's ex-fiancé, Ms. Jackson, was the source of their hostility.

Now Berto's personal chef is taking shots at the personal chef who prepares Mayweather's meals during training camp.  

TMZ Sports spoke with Chef Justine -- who's in charge of Berto's diet as he preps for the September 12th fight -- and she tells us Berto has a major advantage when it comes to cuisine.

"What we are doing over here is 100 times better health-wise than what Floyd's doing," Chef tells us.

She's clearly referring to Chef Q -- who's been handling Mayweather's food for a while -- and recently told us Floyd's been indulging on all sorts of sweets during training camp. 

"I will never ever EVER do what she does," Justine says ... "Her food looks good on the soul food side but I don’t think your heart could last too long eating that all day."

Justine says she's got Berto on a special "Warrior Diet" -- which means no sugar, no grains, no calories wasted. Instead, he'll be eating a lot of "organic and raw foods."

"Andre is working super hard. He is not taking anything lightly to get his mind and body right," Justine says ... "My diet program will be a huge reason why Berto will win."