But their whistles stayed silent, as Zadek celebrated her first on-stage triumph.
"At the end even they applauded and were my fans," recalls the 95-year diva with a chuckle, as she recounts a life of improbable turns from the time she fled Nazi Germany to that first performance in Vienna that launchedthe former shoe sales clerk's stellar opera career.
Sixty-five years later, Vienna has morphed from what she calls a post-war "nest of Nazis" replete with die-hard Hitler supporters into a city that has worked to reckon with its past. Austria's capital has compensated thousands of relatives of Holocaust victims and frequently honors their memory. After decades or denial, Vienna's municipal government now freely recognizes that the city and the nation were Hitler's eager accomplices.
As for Zadek, the city she once despised as part of Hitler's evil empire has long become a home she says she would never leave and one that is proud to call her its own. She has been showered with medals, granted high honorary titles and a singer's competition named after her 13 years ago has turned into an international launching pad for future opera stars.
"I live the life," she exults, eyes twinkling behind rimless glasses as she serves coffee in her high-ceilinged apartment at Vienna's tony 19th district. "I don't feel a trace of anti-Semitism. And I have long forgiven Vienna was a wonderful audience from the first moment on."
With even Viennese Nazi sympathizers charmed by that first performance, Zadek was unstoppable. By the time she stopped singing and turned to teaching in 1971, the spunky soprano was one of the world's leading divas, with 60 roles under her belt and thousands of appearances at the world's greatest opera houses.She still teaches today, equating voice coaching with a personal mission to pass on what she knows to a new generation.
"If I had to give an accounting of myself up above and were asked 'what have you achieved,' then I would say, 'I have trained good voice teachers,'" she says.
The way to Vienna and operatic stardom was perilous.
It began in 1934, in Poznan. Now Polish, the city was then part of Germany, and like other German communities it was gripped by growing anti-Semitism that made life more and more intolerable for Jews.
"I was told often enough what a Jew is, including that they had deformed brains," she said.Kids were taken on school outings to see the Fuehrer and on one such occasion "I had the 'privilege' of seeing Herr Hitler, the 'joy' of breathing in his aura an ugly little gnome who did nothing else but scream with a face contorted by hate!"
One day, it all came to a head: "I knocked out a few front teeth of a school-mate after she said 'it stinks like Jews here,'" she said. "From that second on I had to leave Germany or I would have been jailed."
Zadek initially fled to Berlin; then a year later, at age 17, to what was then Palestine. She worked first in an orphanage, living in a small room with 16 of her charges before training as a pediatric nurse at a hospital.Life was hard, but safe unlike at home, where the Nazi vise was tightening around the Jews who remained.
Her father's four-story shoe emporium was destroyed in 1938 as Nazis rampaged, thrashing and torching Jewish businesses in what became known as "Kristallnacht" the "Night of Broken Glass." He was sent to a concentration camp shortly afterward.
Jews could still leave if they had elsewhere to go, and Zadek got her family visas for Palestine after her father was released. He opened a small shoe store and she left the hospital to work for him. At night she studied voice she had wanted to sing opera from childhood, but she said "nothing sang in me" from the time she fled Germany until that joyful family reunion.
"Then everything in me started singing again."
Her teachers were Austria's and Germany's best renowned Jewish voice coaches who fled to Palestine. At the same time, there were few prospects. There was no opera house and Zadek says that in British-ruled Palestine, singing in German, the language of much of the world's greatest operas, was prohibited.
Once the war was over, the young singer was accepted at the Zurich Conservatory. She paid her way to Europe on a British troop ship by singing to the soldiers.In Switzerland, she worked as an au pair, studied voice and through a chance acquaintanceship suddenly found herself singing for Vienna State Opera Director Franz Salmhofer, who invited her to come to a city still closely identified with the Nazis, even if the party had been banned after the war.
"I would have returned to Berlin as well, because I had only one goal; to become an opera singer," she said. "At the same time, I went through unbelievable emotional turmoil, not only because of my own doubts but because of what my family and friends in Palestine said. I was bad-mouthed from top to bottom for entering this 'nest of Nazis.'"
Looking back, she sees that her return was more than just about singing opera.
"I had to show that Jews don't stink, that they don't have hunched backs, long noses or anything else" branding them as subhuman under the Nazis, she said. "These young people aged 17, 18, who grew up under Hitler, had never seen a Jew in their lives! And then suddenly this young and good-looking woman comes onto the stage and then proceeds to sing beautifully and they ask 'this is a Jew?'"
"Forget the old Nazis," she said. "But I hope I was able at least to change the image ... for the youth."
The next day, she signed a contract with the Vienna opera that ended only when she stopped singing more than 20 years later.Top engagements followed at the Met in New York, London's Covent Garden and opera houses and festivals in Rome, Paris, Munich, Salzburg, Edinburgh and elsewhere, keeping her performing 12 months of the year and establishing her as one of her era's top divas.
As she progressed, so did Austria from being home to the "nest of Nazis" ready to destroy her career for being Jewish, to a country that is proud to call her its own.
"Today? I am never attacked," she says, with a laugh. "I am overwhelmed with honors."