PROFESSOR Ma Zhiying is a food safety expert, so he pays a lot of attention to the food scandals that have rocked Shanghai and China in the past few years. He's especially interested in helping consumers learn to eat a safe and healthy diet.

Ma is technical director of the Shanghai Food Research Institute and director of Shanghai Food Association Committee of Experts. He has more than 30 years' experience in food safety.

Overshadowing all scandals was the San Lu baby milk powder scandal in 2008 when melamine, an industrial chemical, was added to raw milk to fake its protein level, making it appear protein-rich. At least six infants died nationwide and at least 300,000 were sickened.

Most recently, five scandals in the past three months have dulled the image of Shanghai-based Bright Dairy, one of the city's most recognized and trusted brands selling a range of dairy products. A cheese product for children was recalled after an unauthorized additive was found. In September it had to recall batches of sour milk.

The company has issued apologies, saying it fixed the problem and promised to restore customer confidence.

A government safety regulator called on Professor Ma to investigate and he called the case of contaminated milk "an accident of production."

"The tap of a cleaning valve joining a production pipe is supposed to be closed, but it opened by accident," Ma tells Shanghai Daily about Bright Dairy's contaminated milk. "It was caused by a nonhuman error beyond control."

Many people are looking for guidance on what's safe to eat, and there's all kinds of material published in books and on the Internet. It can be bewildering. Ma himself has published two guides that he says will help people eat a safe and healthy diet: "What Is Edible - Strategy of Dietary Safety" (2011) and "What Is Edible - Strategy of Purchasing Safe Food" (2012). Both are in Chinese.

"People always ask me many of the same questions on eating safe and healthy," 63-year-old Ma says. "I want to let them know how to protect themselves."

Ma introduces the concept of "risk analysis," saying it's important to judge whether food is harmful and know how to identify injurious ingredients and the harm they cause.

"Since harmful additives can affect health after an overdose, the amount of all permitted ingredients' upper limits must be set clearly," Ma says. "Dose determines toxicity."

Professor Ma graduated in biochemical engineering from East China University of Science and Technology. Acknowledged for his expertise in research into food biochemistry, food technology and food safety, Ma is a consultant to the Shanghai government departments supervising food safety.

Ma emphasizes that while all injurious substances cannot be completely removed from food, consumers can minimize the potential harm caused by food.

Balance in diet

Asked about avoiding potentially harmful additives and ingredients, Ma recommends a diverse diet to achieve nutritional balance. "No matter how delicious it is, dietary bias is not wise," Ma advises.

Too much of a certain kind of food containing harmful ingredients can cause long-term problems of toxicity, he says. "For example, someone favors shark's fin particularly, which contains heavy metals like cadmium and mercury. Eating occasionally isn't dangerous but a habitual fin's eater definitely are more likely to suffer from mercury poisoning."

A well-balance diet is the best way to "spread risk" and provides comprehensive nutrition, he says. Variety is his personal golden rule of eating.

"Every time I have lunch, my colleagues like to gather around to see what I eat because they think I'm the food expert," Ma says. "But they find there's no so-called 'secret' of my diet since I eat various foods."

Ma's first book "Strategy of Dietary Safety" was so popular that readers told him they wanted more information, especially about how to buy food that's safe and healthy.

Here are a few tips:

? Don't be tempted to buy things on the cheap, referring to old, possibly mildewed rice. "Rice vendors offer much cheaper price, but you never know where his rice come from.

? Buy food from established channels, such as supermarkets.

? Try to get best-known brands. Though the Bright Dairy case makes people question the big name's reputation, "famous brands are always the most trustworthy."

? Read food labels about nutrition. "Carbohydrates, protein and calcium ... a consumer should know how these nutrients benefit our health."

Beyond the obvious rules, Ma learns from experience and pays close attention to his food looks, tastes and smells.

"I once went out for a hot pot dish," Ma says. "But soup looks suspiciously bright red an hour after boiling, so I felt there must be something wrong. I took the soup sample back with me and carried out an experiment. The results justified my suspicion that a chemical dye had been added to the soup."

How to select fresh rice

? Appearance

Fresh, round-grained rice is translucent white, immature rice is a bit jade green. Germs of fresh rice are ivory or faint yellow; rice that's stocked for long is darker or brownish with white grooves on the surface.

? Smell

Rub the grain and smell it. Fresh rice has a faint smell, delicate and natural, not pungent. Old rice smells like rice bran.

? Touch

Fresh rice feels like smooth glass beads while old rice feels coarse. Mineral oil may be added to old rice to make it seem fresh.

? Taste

Fresh uncooked rice tastes harder than old.

How to select eggs

? Look against light

Look for an air chamber, the smaller the chamber, the fresher the egg. If it looks dim and dark inside, the egg isn't good.

? Look at the surface

A fresh egg's surface forms a layer of white powder after being exposed to air. Stocked eggs have no such layer.

? Shake

Fresh eggs feel heavier than older, stocked ones. Shake it a bit, if there's no sound, it's fresh. If not, don't buy it.

? Check

Check the date of production. Eggs can be kept for 45 days at 2-5 degrees Celsius, 25 days at room temperature.