Although offered a job as an assistant chemist by the Washington state government, Orosa returned to the Philippines in 1922. She initially taught home economics at the
Centro Escolar University, and later transferred to the Philippine Bureau of Science's
food preservation division. Beginning in 1926, Orosa visited China, Japan, Hawaii, Britain, the Netherlands, France, Germany, Italy and Spain to research food technology and
preservation. She toured more than 50 canning factories. After she returned to the Philippines, she was appointed the head of the Food Preservation Division and, later, the Home Economics Division of the Bureau of Science. By 1934, Orosa was in charge of the Plant Utilization Division at the Bureau of Plant Industry. Orosa wanted to help the Philippines become self-sufficient, as well as empower Filipino families. She organized
4-H clubs in the islands (which had more than 22,000 members by 1924), and traveled into the
barrios to teach women how to raise chickens, preserve local produce, and plan healthy meals. With the help of this organization, she and numerous protesters visited various communities throughout the Philippines to educate women on innovative methods of food preparation and preservation. Orosa invented the
palayók oven to enable families without access to electricity to bake, and developed recipes for local produce, including cassava, bananas, and coconut. Imported
tomato ketchup, introduced by the Americans, was popular but expensive. Orosa invented a ketchup made with bananas and other local ingredients, instead of tomatoes. Banana ketchup became a favorite condiment and cooking ingredient in the archipelago. She also developed wines and
calamansi nip, a desiccated and powdered form of the citrus fruit used to make reconstituted calamansi juice, banana ketchup, and in other recipes. Using both her local and technical knowledge, Orosa made culinary contributions and taught proper preservation methods for native dishes such as
adobo, dinuguan, kilawin and
escabeche. During
World War II, Orosa used her food science background to invent Soyalac (a protein-rich powdered soybean product) and
Darák (a
rice bran powder rich in
thiamine and other vitamins which could also treat
beri-beri). She also became a captain in Marking's Guerrillas, a Filipino guerrilla group organized by Marcos "Marking" V. Augustín. The guerrillas helped United States forces fight the occupying Imperial Japanese troops, and employed carpenters to insert Soyalac and Darák into hollow bamboo sticks, which were then smuggled to civilians imprisoned at the
University of Santo Tomas and in Japanese-run
prisoners of war camps in
Capas, Tarlac and
Corregidor. The powders saved the lives of many starving imprisoned guerrillas and U.S. soldiers. Her "Tiki-Tiki" cookies (also made using Darák) saved many civilian lives during wartime food shortages. ==Death and legacy==