DS is 8 and possibly the fartiest child I have ever met 
He farts loudly and finds it hilarious, and frankly they often stink.
He also has autism so the social thing of not farting in public just isn't sinking in. He has enough social challenges without being the smelly kid, so I'm really desperate to find some ways to reduce this.
He eats a mostly vegetarian diet (but has fish and chips for school dinner on Fridays). He eats pulses maybe 3 times a week and refuses all green veg except raw brocolli dipped in ketchup (so not like he's eating endless cabbage!). In fact the only cooked veg he will knowingly eat are peas, sweetcorn, and potatoes, though he likes raw veg sticks and loves fruit, and I sneak veg into pasta sauces and blended soups. His diet is limited but still reasonably well balanced. We have mostly wholemeal bread (about 70% of the time, with the odd nice crusty white baguette etc) but white rice/pasta/couscous.
Typical days food is breakfast - oats with raisins and full fat cows milk. Lunch - packed lunch of cheese or quorn ham roll, some breadsticks, cucumber and cherry tomatoes, piece of fruit, flapjack, or school lunch of typical school dinner food (carbs with more carbs usually). Dinner - things like pasta pesto/baked potatoes/soup and usually a fruit yoghurt (always a live yoghurt) to follow.
However his diet doesn't seem to make much difference - it isn't noticeably worse after eggs or beans for example. When we tried to go dairy free last year it got a lot worse on soya/oat milk so we scrapped that idea as soon as we made the connection. But other than that, it just seems random - he has days where its not a problem and days where he trumps away loudly and can clear a room.
I suspect he swallows a lot of air while eating due to a) tongue tie that wasn't properly corrected as a baby and b) eating too fast and never stopping talking! I'm working on that but obviously it's not an instant fix.
Are there any supplements or dietary changes I could try? Bearing in mind his autism means he's wary of new foods and I'd have to hide any supplement in yoghurt!